-NRLF 


BIOLOGY 

UBRARV 


ANIMALS  FOUND  LIVING  TOGETHER  IN  SHALLOW  INLETS  FROM 
THE  SEA,  LONG  ISLAND  SOUND 


A  TEXT-BOOK 


IN 


GENERAL   ZOOLOGY 


BY 


HENRY  R.  LINVILLE,  PH.D. 

HEAD  OF  THE  DEPARTMENT  OF  BIOLOGY,  DE  WITT  CLINTON 
HIGH  SCHOOL,  NEW  YORK  CITY 


HENRY  A.  KELLY,  Pn.D. 

DIRECTOR  OF  THE  DEPARTMENT  OF  BIOLOGY  AND  NATURE  STUDY 
ETHICAL  CULTURE  SCHOOL,  NEW  YORK  CITY 


Two  Hundred  Thirty-Three  Illustrations 


GINN  &  COMPANY 

BOSTON  •  NEW   YORK  •   CHICAGO  •  LONDON 


BIOLOGY 

LIBRARY 

G 


ENTERED  AT  STATIONERS'  HA  LI. 


COPYRIGHT,  1906 
BY  HENRY  K.  LINYILLE  AND  HENRY  A.  KELLY 


ALL  RIGHTS  RESERVED 
06.5 


GINN    &    COMPANY  •  PRO- 
PRIETORS  •  BOSTON  •  U.S.A. 


PREFACE 

In  offering  to  the  educational  public  this  text-book  in  general 
zoology,  with  its  accompanying  suggestions  for  laboratory  work, 
we  desire  to  explain  in  brief  the  method  of  construction  we  have 
followed. 

The  treatment  of  the  phyla  is  in  a  descending  order  from  the 
Arthropoda  to  the  Protozoa,  and  in  an  ascending  order  from  the 
fishes  to  man.  After  many  years  of  experience  with  classes  of 
young  students  we  believe  that  an  order  of  treatment  resembling 
this  is  likely  to  yield  the  best  results,  although  we  do  not  deny 
that  good  results  may  be  obtained  with  young  students  by  follow- 
ing what  is  sometimes  called  the  "  order  of  evolution,"  beginning 
with  the  Protozoa.  Although  the  chapters  are  interdependent, 
we  think  that  there  is  sufficient  unity  in  each  to  make  it  possible 
for  the  teacher  to  diverge  from  the  order  we  have  employed. 

Whatever  the  order  followed,  it  is  evident  that  recitation  on 
the  chapters  in  the  text-book  should  be  held  only  after  the  pupil 
lias  made  his  study  in  the  laboratory,  for  the  text-book  in  science 
has  its  greatest  usefulness  in  connecting,  extending,  and  illumi- 
nating the  work  of  the  laboratory.  Laboratory  work  brings  the 
pupil  in  touch  with  actual  things,  and  if  the  studies  are  properly 
conducted,  they  will  aid  in  developing  in  the  mind  the  power  of 
independent  judgment.  But  the  young  and  untrained  student 
cannot  build  up  a  conception  of  the  science  of  zoology  from  the 
more  or  less  isolated  data  of  the  laboratory ;  in  this  fact  lies  the 
justification  of  a  text-book  in  zoology. 

The  function  of  the  suggestions  for  laboratory  work  is  to  help 
the  pupil  to  make  the  be*st  use  of  his  time,  and  to  direct  him  in 
such  a  way  that  he  will  become  more  and  more  independent, 
and  be  able  to  study  intelligently  without  detailed  directions. 
It  seems  to  us  that  the  kind  of  directions  given  to  pupils  will 

iii 

152365 


iv  PREFACE 

depend  not  only  on  the  teacher's  training  in  zoology  and  his 
pedagogical  skill,  but  also  011  the  age  and  previous  training  of 
the  pupils.  The  problem  is  a  special  one  for  each  teacher  to 
solve  for  himself.  The  directions  given  in  the  accompanying 
pamphlet,  therefore,  are  to  be  regarded  merely  as  suggestive. 

The  inductive  method  of  presentation,  in  a  necessarily  modified 
form,  has  been  followed  in  the  earlier  chapters  of  the  text-book, 
as  being  the  natural  mode  of  approach  to  a  new  subject  based 
upon  laboratory  work.  After  the  study  of  the  red-legged  locust, 
for  example,  another  animal  that  has  easily  recognizable  rela- 
tionship to  this  form  is  considered.  Not  until  all  the  selected 
representatives  of  the  Orthoptera  have  been  described,  are  the 
characters  of  the  order  mentioned.  By  that  time  the  pupil's 
mind  is  ready  for  the  definition  of  Orthoptera.  The  conceptions 
of  the  larger  groups  of  invertebrate  classes  and  phyla  are  devel- 
oped in  the  same  manner. 

It  has  been  our  earnest  endeavor  to  present  all  the  important 
aspects  of  zoology  in  a  well-balanced  account.  The  basis  of  the 
subject-matter  in  a  text-book  on  zoology  is  necessarily  morpho- 
logical. The  pupil  must  have  some  understanding  of  the  appear- 
ance of  animals  and  their  organs  before  he  can  be  supposed  to 
think  clearly  regarding  the  uses  of  the  organs  or  the  relation  of 
the  animals  to  their  environment.  We  have  described  the  appear- 
ance of  nearly  all  the  animals  mentioned.  In  certain  selected 
cases  we  have  described  the  structure  and  the  functions  of  the 
systems  of  internal  organs,  and  the  development  of  the  individ- 
ual ;  and  in  appropriate  connections  we  have  spoken  of  the 
economic  importance  of  animals,  and  have  given  brief  sketches 
of  the  geographical  distribution  and  the  geological  history  of 
races.  The  rapidly  developing  science  of  comparative  psychology 
is  now  sufficiently  precise  to  justify  the  inclusion  in  a  work  of 
this  kind  of  some  of  the  important  studies  of  the  mental  behavior 
of  animals.  We  hope  that  the  facts  selected  will  give  a  general 
notion  of  the  increasing  complexity  of  the  mental  life  in  the 
higher  animals.  We  have  also  presented  in  as  simple  a  way 


PREFACE  v 

as  possible  the  doctrine  of  evolution.  Finally,  the  last  chapter 
deals  with  the  historical  development  of  the  science  of  zoology. 
It  should  aid  in  giving  the  pupil  the  necessary  perspective  for 
appreciating  the  processes  by  which  this  organized  body  of 
knowledge  came  into  existence. 

The  principles  of  physiology  are  reserved  for  full  explanation 
in  the  study  of  the  earthworm  in  Chapter  XVI.  We  desire  here 
to  express  our  deep  obligation  for  the  inspiration  and  example 
of  a  similar  study  presented  in  General  Biology  by  Professors 
W.  T.  Sedgwick  and  E.  B.  Wilson.  We  are  indebted  to  them 
and  their  publishers  for  several  figures  illustrating  the  develop- 
ment of  the  earthworm.  Our  purpose  in  delaying  the  scientific 
treatment  of  the  principles  of  physiology,  instead  of  discuss- 
ing them  in  the  first  chapters,  is  a  double  one.  In  the  first 
place,  too  much  abstraction  at  the  beginning  of  an  exposition 
is  likely  to  prove  discouraging  to  even  a  willing  student ;  in  the 
second  place,  the  conception  of  physiological  processes,  it  seems 
reasonable  to  believe,  can  be  formed  best  after  the  learner  has 
some  knowledge  of  systems  of  organs,  including,  of  course, 
an  elementary  knowledge  of  their  uses.  It  then  matters  little 
whether  the  student  learns  the  more  detailed  facts  of  physiology 
from  the  earthworm  or  from  some  other  animal,  and  it  even 
matters  little  whether  or  not  he  actually  sees  all  the  organs  in 
the  animal  where  the  processes  are  described  as  taking  place. 

We  believe  that  the  attention  given  in  this  book  to  the  subject 
of  animal  ecology  will  prove  to  be  justified.  Although  the  eco- 
logical sections  are  set  off  from  the  other  topics,  it  should  not 
be  forgotten  that  ecology,  or  the  relation  of  organisms  to  their 
environment,  has  significance  only  when  the  subject  is  considered 
from  the  standpoint  of  the  adjustment  or  the  adaptation  in  the 
form  of  the  parts  of  organisms  to  the  life  they  carry  on. 

We  have  been  to  considerable  pains  to  produce  original  figures 
that  should  be  comprehensive  as  well  as  accurate,  and,  where  the 
subject  permitted,  artistic.  In  this  we  have  been  assisted  by 
three  gentlemen  whose  ability  is  e'vident  in  their  work:  Mr.  S.  F. 


vi  PREFACE 

Denton,  of  Wellesley,  Mass.,  Mr.  L.  H.  Joutel,  of  New  York  City  ; 
and  Mr.  E.  N.  Fischer,  of  Jamaica  Plain,  Mass.  Mr.  Denton 
made  the  drawings  of  the  vertebrate  dissections  and  the  external 
view  of  the  lizard  and  Oniscus.  Mr.  Joutel  made  the  drawings 
of  the  insects  and  all  the  invertebrate  dissections.  Mr.  Fischer 
executed  the  drawings  of  all  the  marine  invertebrates  shown 
in  their  natural  environment,  and  also  the  ecological  studies 
of  the  pond-snail,  the  garden-slug,  the  garden-spider,  the  leech, 
the  fresh-water  mussel,  and  the  fresh-water  sponge,  besides 
copying  many  figures  from  publications.  Mr.  Win.  T.  Oliver,  of 
Lynn,  Mass.,  made  the  numerals  and  the  leader-lines  for  all  the 
drawings. 

We  desire  to  acknowledge  the  kindness  of  Professor  H.  C. 
Bumpus,  Director  of  the  American  Museum  of  Natural  History, 
arid  of  Professor  H.  F.  Osborn,  Curator  of  Vertebrate  Paleontol- 
ogy, American  Museum,  in  permitting  us  to  make  selections  from 
numerous  photographs.  Mr.  C.  William  Beebe,  of  the  Xew  York 
Zoological  Park,  supplied  us  with  photographs  of  many  verte- 
brates and  some  marine  invertebrates.  Several  photographs  in 
different  chapters  are  from,  the  authors'  own  collections.  To 
the  following  publishers  we  acknowledge  the  privilege  of  using 
figures:  American  Book  Company;  D.  Appleton  &  Co.;  G-.  W. 
Crane  &  Co. ;  Doubleday,  Page  &  Co. ;  Henry  Holt  &  Co. ;  McClure, 
Phillips  &  Co. 

It  is  our  hope  that  the  quotations  which  introduce  the  chap- 
ters will  serve  to  suggest  to  the  imagination  of  young  students 
the  poetic  side  of  animal  life  and  of  nature  generally.  For  some 
of  the  best  quotations  we  are  indebted  to  the  search  made  by 
personal  friends. 

We  are  especially  grateful  to  several  zoologists  who  have  read 
various  portions  of  the  manuscript  critically  :  Professors  G.  H. 
Parker  and  W.  E.  Castle,  of  Harvard  University  ;  Professor  J.  H. 
Comstock,  of  Cornell  University;  Professor  H.  8.  Jennings,  of  the 
University  of  Pennsylvania ;  Professor  M.  A.  Bigelow,  of  Teachers 
College,  Columbia  University  ;  Dr.  J.  A.  Allen,  Mr.  Frank  M. 


PREFACE  vii 

Chapman,  and  Professor  R.  W.  Tower,  of  the  American  Museum 
of  Natural  History  ;  and  Dr.  F.  B.  Sumner,  of  the  College  of  the 
City  of  New  York.  For  suggestions  in  regard  to  some  of  the 
more  important  drawings  we  extend  our  thanks  to  Professors 
E.  L.  Mark,  G.  H.  Parker,  W.  E.  Castle,  Dr.  H.  W.  Rand,  and 
Dr.  W.  McM.  Woodworth,  of  Harvard  University ;  to  Professor 
J.  S.  Kingsley,  of  Tufts  College  ;  and  to  Professor  C.  W.  Hargitt, 
of  Syracuse  University. 

Certain  little-known  species  have  been  identified  for  us  in  the 
tunicates,  leeches,  holothurians,  crustaceans,  gasteropods,  and 
sponges,  respectively,  by  the  following  :  Professor  W.  E.  Ritter, 
of  the  University  of  California  ;  Professor  J.  Percy  Moore,  of 
the  University  of  Pennsylvania  ;  Professor  H.  L.  Clark,  of  Olivet 
College  ;  Dr.  Walter  Faxon,  of  the  Museum  of  Comparative 
Zoology,  Cambridge,  Mass. ;  Dr.  L.  P.  Gratacap,  of  the  American 
Museum  of  Natural  History  ;  Professor  H.V.Wilson,  of  the  Uni- 
versity of  North  Carolina  ;  and  Mr.  Edward  Potts,  of  Philadelphia. 

To  Mr.  D.  C.  MacLaren,  of  the  DeWitt  Clinton  High  School, 
we  are  very  much  indebted  for  transposing  into  equivalent  Eng- 
lish letters  the  roots  of  the  Greek  derivatives. 

THE  AUTHORS 


CONTENTS 

CHAPTER  PAGE 

I.    THE  COMMON  RED-LEGGED  LOCUST 1 

II.    THE  ALLIES  OK  THE  RED-LEGGED  LOCUST:  ORTHOPTERA     15 

III.  THE    MAY-FLIES    (PLECTOPTERA)    AND    THE    DRAGON- 

FLIES    (Ol)ONATA) 25 

IV.  THE  BUGS:  HEMIPTERA 30 

V.    THE  BEETLES:  COLEOPTEKA 37 

VI.    THE  BUTTERFLIES  AND  MOTHS:  LEPIDOPTERA    ...     4(5 

VII.    THE  FLIES:   DIPTEHA 58 

VIII.    THE  ANTS,  BEES,  AND  WASPS  :  HYMENOPTERA   .     .     .     05 

IX.    THE  INSECTS:  HEXAPODA 81 

X.    THE  DOCTRINE  OK  EVOLUTION 101 

XL    THE  SPIDERS  AND  ALLIES  (ARACIINIDA)  AND  THE  CEN- 

TIPEDS    AND    MlLLEPEDS    (MYRIAPODA)         .        .        .        .110 

XII.    THE  CRAYFISH 125 

XIII.  THE  JOINTED-FOOT  ANIMALS:  ARTHROPODA    .      .v    .      .  138 

XIV.  THE  CLAM  AND  OTHER  BIVALVES:  PELECYPODA     .     .  157 
XV.  ALLIES  OF  THE  PELECYPODA:  MOLLUSCA    .      .      .  ".      .  177 

XVI.    THE  EARTHWORM 195 

XVII.    ALLIES  OF  THE  EARTHWORM:  VERMES 222 

XVIII.    THE  STARFISH  AND  SOME  ALLIES  :  ECHINODERMA  .x    f  230 
XIX.    THE  SEA-ANEMONE  AND  SOME  ALLIES:  CCELENTERA    .  252- 
XX.    THE   FRESH-WATER   SPONGE  AND  SOME  ALLIES: 

PORIKERA .*     ....  273 

XXI.    AMCEBA  AND  SOME  ALLIES:  PROTOZOA 280 

XXII.    THE  EVOLUTION  OF  INVERTEBRATES  AND  THE  ANCESTRY 

OF  THE  VERTEBRATES  ....." 292 

XXIII.    THE  YELLOW  PERCH 305 

ix 


x  CONTENTS 

CHAPTER  PAGE 

XXIV.  THE  ALLIES  OE  THE  PERCH:  PISCES 310 

XXV.  THE  GREEN  FROG 327 

XXVI.  THE  ALLIES  OE  THE  FROG  :   AMPHIIJIA 339 

XXVII.  THE  PINE-LIZARD  AND  ITS  ALLIES:   REPTILIA       .     .  348 

XXVIII.  THE  DOMESTIC  PIGEON 304 

XXIX.  THE  ALLIES  OF  THE  PIGEON:  AYES 374 

XXX.  THE  GRAY  SQUIRHEI 398 

XXXI.  THE  ALLIES  OF  THE  SQUIRREL:  MAMMALIA      .      .      .  408 

XXXII.  THE  HISTORICAL  DEVELOPMENT  OF  ZOOLOGY    .     .      .  430 

INDEX  .  4f)3 


GENERAL    ZOOLOGY 

CHAPTER    I 
THE   COMMON   RED-LEGGED   LOCUST 

Though  I  watch  their  rustling  flight, 

I  can  never  guess  aright 

Where  their  lodging-places  are  ; 

'Mid  some  daisy's  golden  star, 

Or  beneath  a  roofing  leaf, 

Or  in  fringes  of  a  sheaf, 

Tenanted  as  soon  as  bound.  —  EDITH  M.  THOMAS. 

Habitat  and  Distribution.  Locusts  are  found  almost  every- 
where in  the  United  States,  usually  in  fields,  meadows,  and 
along  roadsides.  They  are  often  spoken  of  as  grasshoppers, 
but,  as  we  shall  see  later,  they  differ  from  the  true  grass- 
hoppers in  several  important  particulars.  The  species  (see 
p.  95)  which  heads  this  chapter  is  one  of  the  most  widely 
distributed  of  the  insects  to  which  the  name  locust  is  cor- 
rectly applied.  It  is  known  to  naturalists  as  Melan'oplus l 
fe'mur-ru'brum.  Its  habitat  (the  locality  where  it  is  naturally 
found)  comprises  grassy  areas  in  almost  every  state  except 
on  the  high  western  plains,  where  its  place  is  taken  by  a 
species  much  resembling  it,  —  the  Rocky  Mountain  locust 
(Melanoplus  spre'tus).  Another  species,  the  lesser  locust 
(Melanoplus  atlan'is),  somewhat  smaller  and  darker  in  color, 
is  also  found  in  nearly  every  part  of  the  country.  These, 
and  several  other  locusts,  are  about  three  centimeters  (a  little 

1  The  first  time  a  scientific  name  is  used,  a  mark  is  placed  after  the 
accented  syllable  as  an  aid  in  pronunciation. 

1 


...........GENERAL   ZOOLOGY 

over  an  inch)  in  length,  and  resemble  each  other  so  closely 
that  the  following  description  will  apply  nearly  as  well  to 
one  as  to  another. 

External  Plan  of  Structure.  The  body  is  made  up  of  a 
series  of  rings,  called  somites  (Fig.  2),  externally  hardened  by 
a  horny  substance,  chitin,  for  protection  of  the  interior  organs. 
The  somites  are  grouped  in  three  clearly  marked  regions,— 
the  head,  thorax,  and  abdomen  (Fig.  2,  1,  2-4,  5).  While  the 
characteristic  appearance  of  a  ring  is  clearer  in  the  abdo- 
men than  elsewhere,  it  is  nevertheless  true  that  the  head  and 
thorax  are  made  up  of  several  somites,  much  altered  and 
pressed  together.  The  head  probably  consists  of  at  least  five 
somites,  of  which  four  bear  appendages,  the  feelers,  or  anten- 
na? (Fig.  2,  0);  the  jaws,  or  mandibles  (Fig.  1,  2;  Fig.  2,  8); 
the  first  maxilla?  (Fig.  1,  4) ;  and  the  second  maxilla*  (Fig.  1,  5). 
The  thorax  plainly  consists  of  three  somites,  on  each  of  which 
is  borne  a  pair  of  legs  (Fig.  2,  14, 15, 10).  Ten  somites  can  with- 
out much  difficulty  be  distinguished  in  the  abdomen  (Fig.  2,  5). 
The  external  plan  upon  which  the  locust  is  built  is  thus  seen 
to  be  a  series  of  somites,  of  which  the  anterior  (front)  somites 
bear  jointed  appendages  modified  for  various  uses. 

The  Head.  The  short,  several-jointed  antennas  are  organs 
of  touch  and  of  smell,  and,  in  most  insects,  of  hearing  as  well. 
The  maxillas  are  constructed  on  the  plan  of  jaws,  though 
fitted  for  guiding  and  holding  food  rather  than  for  crush- 
ing it.  Each  maxilla  bears  a  short,  several-jointed  "  feeler,"  • 
or  palpus  (Fig.  1,  4,  5  ;  Fig.  2,  9,  11).  The  anterior  boundary  of 
the  mouth  is  a  flap-like  piece,  the  upper  lip,  or  labrum  (Fig.  1,  1; 
Fig.  2,  7) ;  and  the  posterior  (hind)  boundary  is  made  by  the 
union  of  the  bases  of  the  second  maxilla  (Fig.  1,  5),  forming 
a  flap  called  the  lower  lip,  or  labium  (Fig.  2,  10). 

On  the  sides  of  the  head  are  large,  oval,  compound  eyes 
(Fig.  2,  12),  composed  externally  of  a  number  of  transparent 
divisions,  facets,  each  of  which  has  beneath  it  the  necessary 


THE  COMMON   RED-LEGGED  LOCUST 


structures  for  sight,  so  that  the  whole  may  be  regarded  as 
a  mosaic  of  single  eyes.  In  addition,  there  are  simple  eyes,  or 
ocelli  (Fig.  2, 13),  placed 
in  the  form  of  a  triangle 
on  the  front  of  the  head. 
Notwithstanding  these 
two  kinds  of  eyes,  it  is 
doubtful  whether  the 
locust  is  able  to  per- 
ceive well  the  outlines 
of  objects,  or  to  dis- 
tinguish much  except 
light  and  movement. 
The  ocelli  probably  do 
not  perceive  objects  at 
a  greater  distance  than 
a  few  inches,  nor  the 
compound  eyes  at  a 
greater  distance  than  a 
few  feet.  It  has  been 
surmised  from  the 
structure  of  the  com- 
pound eyes  that  each  facet  perceives  only  a 
field  of  vision. 

The  Thorax.  The  first  somite  of  the  thorax,  called  the  pro- 
thorax  (Fig.  2,  2),  bears  the  first  pair  of  legs.  It  is  free  from 
the  rest  of  the  thorax.  The  dorsal  surface  (Latin,  dorsum, 
back)  is  thickened  and  raised  into  a  ridge ;  the  sides  (lateral 
surfaces)  are  also  thickened,  and  the  whole  forms  a  protective 
shield  or  collar.  The  second  somite,  the  mesothorax  (Fig.  2,  3), 
bears  the  second  pair  of  legs ;  to  the  third,  or  metathorax 
(Fig.  2,  4),  the  last  pair  of  legs  is  attached.  Each  leg  is  com- 
posed of  a  number  of  divisions,  or  segments,  of  which  the 
principal  are  the  thick  femur  (Fig.  2,  14,  15,  16 ;  Fig.  3,  5) 


FIG.  1.   Mouth-Parts  of  Red-Legged  Locust, 
x  4 

1,  labrum;  2,  mandible;  3,  hypopharynx ;  4,  first 
maxilla  with  its  palpus;  5,  second  maxillre 
with  palpi 

jmall  part  of  the 


4  GENERAL   ZOOLOGY 

and  the  spiny  tibia  (Fig.  3,  o).  Each  leg  ends  in  a  series  of 
three  segments,  forming  the  tarsus  (Fig.  3,  7),  the  last  segment 
of  which  bears  two  claws  (Fig.  3,  8),  with  a  pad,  the  pulvillus 
(Fig.  3,  9),  between  them. 

Of  the  two  pairs  of  wings  (Fig.  2,  17,  18),  the  first  is  attached 
to  the  surface  of  the  mesothorax,  the  second  to  the  m eta- 
thorax.  The  anterior  pair  is  somewhat  hardened,  forming 
protective  covers  for  the  more  delicate  posterior  wings,  which 
are  folded  like  a  fan  beneath  them.  The  latter  only  are  used 
in  flight.  The  wings  are  simple  extensions  of  the  body-wall, 
and  not  jointed  appendages  like  the  legs.  On  the  sides,  just 
beneath  the  posterior  edge  of  the  collar  on  the  prothorax,  is 
a  pair  of  breathing  openings,  or  spiracles  (not  shown  in  the 
figure).  Two  spiracles  are  placed  just  above  the  junction  of 
the  second  pair  of  legs  (Fig.  2,  20),  and  the  abdomen  bears 
eight  pairs  along  the  sides  (Fig.  2,  21,  22). 

The  Abdomen.    The  first  abdominal  somite  is  much  larger 

o 

than  the  others,  though  it  does  not  form  a  complete  ring, 
owing  to  the  space  occupied  by  the  cavities  for  the  insertion 
of  the  hind  legs.  Each  side  of  this  somite  bears  an  oval  spot 
consisting  of  a  thin  skin  stretched  across  a  small  cavity  and 
connected  with  a  nerve,  the  whole  forming  an  ear,  or  auditory 
apparatus  (Fig.  2,  19).  The  end  of  the  abdomen  in  the  female 
is  more  tapering  than  in  the  male,  and  is  furnished  with  two 
pairs  of  blunt  spines,  which  form  an  egg-laying  instrument,  or 
ovipositor  (Fig.  3,  36,  37). 

The  Digestive  System.  After  this  brief  review  of  the  main 
features  of  the  external  anatomy  of  the  locust,  we  turn  our 
attention  to  the  organs  of  the  interior.  And  first,  owing  to 
its  size  and  the  ease  with  which  its  parts  may  be  examined, 
we  may  consider  the  digestive  system.  The  function  of  the 
digestive  system  of  an  animal  is  to  prepare  the  food  for  use 
by  the  different  organs  of  the  body.  In  the  locust  the  organs 
of  digestion  are  the  food-tube,  or  alimentary  canal,  and  its 


6  GENERAL   ZOOLOGY 

accessory  organs,  the  salivary  glands  (Fig.  3,  14)  and  gastric 
cceca  (gastric,  pertaining  to  the  stomach ;  caeca,  pi.  of  caecum, 
a  pouch  or  cavity  open  only  at  one  end,  Fig.  3,  1-5,  10). 

The  alimentary  canal  is  a  long  tube  extending  through  the 
body  and  variously  modified  in  the  course  of  its  extent.  The 
first  division  is  the  mouth,  guarded  on  each  side  by  the  later- 
ally moving  mandibles.  Between  the  mandibles,  and  arising 
from  the  inner  side  of  the  labium,  is  a  short  brown,  tongue- 
like  organ,  the  liypopharynx  (Fig.  3, 12  ;  Fig.  1,  3).  At  the  base 
of  the  hypopharynx  opens  the  tube  from  the  several  pairs  of 
salivary  glands.  A  portion  of  the  slightly  convex  surface  of 
the  inner  side  of  the  labrum  is  the  epipharynx,  the  seat  of  the 
sense  of  taste. 

Beyond  the  mouth  the  alimentary  canal  continues  as  a  short 
curved  oesophagus  (Fig.  3,  13),  which  leads  to  a  large  crop, 
armed  with  rows  of  spine-like  teeth.  Posterior  to  the  crop 
is  a  very  small  gizzard,  also  furnished  with  spines,  opening 
directly  into  a  large,  thin-walled  stomach  (Fig.  3,  17).  At  the 
anterior  end  of  the  stomach  are  attached  the  six  tubular 
gastric  cseca,  closed  at  one  end  but  opening  into  the  stomach 
at  the  other.  Beyond  the  stomach  the  alimentary  canal  con- 
tinues as  a  slightly  coiled  tube,  the  intestine  (Fig.  3,  19),  and 
ends  dorsally  at  the  anal  opening  (Fig.  3,  20). 

The  functions  of  these  different  parts  are  as  follows,  The 
food,  after  being  crushed  by  the  mandibles  and  moistened  by 
the  saliva,  enters  the  crop,  where  it  is  subjected  to  the  action 
not  only  of  the  saliva  but  also  of  a  fluid  from  the  gastric  ceeca. 
The  "  molasses  "  thrown  out  from  the  mouth  as  a  defensive 
fluid  by  the  locust,  when  handled,  consists  of  partially  digested 
food  from  the  crop,  mixed  with  the  digestive  fluids.  When 
sufficiently  dissolved  and  changed  chemica%,  the  food  filters 
through  the  spines  of  the  gizzard  into  the  stomach,  where  it 
is  further  acted  upon  by  another  digestive  fluid.  The  thin 
walls  of  the  stomach  allow  the  particles  of  prepared  food  to 


THE  COMMON   KED-LEGGED  LOCUST  7 

pass  through  and  mingle  with  the  blood  in  the  general  body- 
cavity.  This  process  is  called  absorption.  The  anterior  part 
of  the  intestine  is  thin-walled,  and  absorption  may  take  place 
there  and  also  in  the  caeca.  The  unused  food-material  is 
removed  from  the  body  by  means  of  the  anal  opening. 

The  Circulatory  System.  When  the  food  has  been  acted 
upon  by  the  various  digestive  fluids,  and  so  changed  that  it 
may  be  used  to  supply  the  different  organs  with  nourishment, 
it  is  distributed  over  the  body  by  the  circulatory  system.  At 
the  same  time  certain  waste  matters  are  taken  away  and  carried 
to  organs  the  function  of  which  is  to  remove  them  from  the 
body.  In  the  case  of  man  and  many  other  animals,  the  circu- 
latory system  is  also  the  means  by  which  oxygen  is  carried  to 
all  the  organs ;  but,  as  we  shall  see  in  a  moment,  this  work  is 
otherwise  provided  for  in  the  locust.  As  soon  as  the  prepared 
food  has  been  absorbed  by  the  walls  of  the  stomach  and  intes- 
tine it  mingles  with  the  blood,  which  flows  through  the  body- 
cavity  in  sinuses  (spaces  between  the  various  organs),  though 
not  in  definite  blood-vessels.  The  blood  is  propelled  by  a 
tubular,  pulsating  vessel,  or  heart  (Fig.  3,  21),  which  extends 
through  the  abdomen  just  beneath  the  dorsal  surface.  On 
account  of  its  position  in  the  body  it  is  often  spoken  of  as 
the  dorsal  vessel.  The  heart  is  prolonged  anteriorly  into  a 
tube  leading  to  the  head,  and  is  partially  divided  by  valves 
into  eight  chambers,  which  permit  the  movement  of  the  blood 
only  from  the  posterior  to  the  anterior  end.  When  the  blood 
has  been  passed  out  into  the  general  body-cavity  it  returns 
through  a  closed  tube  (ventral  sinus)  between  the  muscle 
masses  lying  in  the  lower  (ventral)  part  of  the  body,  and 
reenters  the  heart  through  side  openings. 

The  Respiratory  System.  The  function  of  the  respiratory 
system  is  to  provide  for  a  constant  supply  of  oxygen  for  all 
the  organs  of  the  body.  This  is  accomplished  by  a  system  of 
tubes,  called  tracheae,  communicating  with  the  surface  by  the 


8  GENERAL   ZOOLOGY 

spiracles  of  the  thorax  and  abdomen.  The  trachese  are  con- 
nected and  form  a  network  of  tubes  running  to  all  parts  of 
the  body,  even  out  into  the  legs  and  wings.  They  are  also 
in  connection  with  a  system  of  large  air-sacs  (Fig.  3,  22,  23) 
extending  through  the  body.  The  tracheae  are  kept  perma- 
nently open  by  a  spiral  thickening  of  their  chitinous  lining, 
so  that  air  may  enter  freely  at  all  times.  The  completeness 
of  the  respiratory  system  in  the  locust  is  in  striking  contrast 
to  the  undeveloped  character  of  the  circulatory  system. 

The  Excretory  System.  The  union  of  the  oxygen  taken  in 
during  respiration  with  the  carbon  in  the  body  produces  car- 
bon dioxide, — a  waste  product.  This  leads  us  to  consider  the 
organs  which  assist  in  the  removal  of  materials  which  have 
helped  to  build  up  the  body-substance  and  have  become  so 
changed  chemically  that  they  are  no  longer  useful.  Such 
organs  are  termed  organs  of  excretion.  Besides  carbon  diox- 
ide, important  excretory  products  are  water  and  various  sub- 
stances containing  nitrogen,  hence  called  nitrogenous  wastes. 
The  two  latter  classes  correspond  to  the  material  removed  by 
the  kidneys  of  the  higher  animals. 

Very  little  is  known  of  the  process  of  excretion  in  insects. 
It  has  been  generally  believed  that  the  carbon  dioxide  finds 
its  way  to  the  surface  through  the  trachese.  In  some  cases  it 
probably  escapes  through  the  skin.  Water  and  the  nitroge- 
nous wastes  are  removed  by  malpigJiian  tubes  (Fig.  3,  18), 
which  form  so  prominent  an  object  when  the  body  of  the 
locust  is  first  opened.  They  ramify  through  the  body-cavity 
and  open  into  the  alimentary  canal  at  the  junction  of  the 
stomach  and  intestine,  their  contents  passing  to  the  outside 
with  the  undigested  food  in  the  intestine.  This  undigested 
food  is  not  an  excretion,  using  the  word  in  the  sense  defined 
above,  since  it  has  never  formed  a  part  of  the  body-substance. 
It  has  been  suggested  that  as  the  chitinous  covering  of  in- 
sects is  largely  made  up  of  carbon  and  nitrogen,  the  frequent 


10  GENEBAL   ZOOLOGY 

casting  of  the  skin  (molting)  may  be  an  act  of  excretion  of 
considerable  importance. 

The  Nervous  System.  All  the  processes  just  described, 
even  the  flow  of  blood  and  the  secretion  (formation)  of  the 
digestive  fluids,  are  under  the  control  of  the  nervous  system. 
Through  its  organs  of  sense  the  locust  is  brought  into  touch 
with  the  outside  world  ;  by  its  control  over  the  muscles,  move- 
ments are  made.  The  nervous  system  of  the  locust  consists 
of  a  series  of  connected  nerve  centers,  called  ganglia  (Fig.  3, 
24,  28,  29),  from  which  nerves  are  given  off  to  the  different 
parts  of  the  body.  There  are  two  kinds  of  nerves,  sensory  and 
motor;  the  former  carry  messages  from  the  various  sense- 
organs  to  the  ganglia ;  the  latter  carry  impulses  from  the 
ganglia,  which  result  in  the  contraction  of  muscles  and  move- 
ments of  the  various  organs,  or  of  the  body  as  a  whole. 

The  largest  ganglion  is  in  the  head,  and  is  generally  called 
the  "  brain,"  or,  because  of  its  position  just  above  the  oesoph- 
agus, the  supraoesophageal  ganglion  (Fig.  3,  24).  From  this 
ganglion  pass  the  nerves  which  go  to  the  eyes,  antennae, 
and  labrum.  Two  cords  encircling  the  oesophagus  pass  to  the 
next  ganglion,  which,  owing  to  its  position  just  beneath  the 
oesophagus,  is  called  the  suboesopliageal  ganglion  (Fig.  3,  28). 
This  ganglion  sends  nerves  to  the  mandibles  and  maxillse. 
Both  the  supraoesophageal  and  the  suboesophageal  ganglia 
are  the  seat  of  will  in  the  locust,  and  preside  over  and 
coordinate  the  various  general  movements  of  the  locust's  body. 
It  has  been  shown  that  an  insect  may  live  for  months  with 
the  anterior  of  these  ganglia  destroyed,  if  the  other  is  not 
injured.  The  insect  will  feed  if  food  is  placed  to  its  mouth, 
but  it  loses  the  power  to  go  in  search  of  food.  Of  the  other 
ganglia  three  are  in  the  thorax  and  five  are  in  the  abdomen, 
forming  a  median  chain  resting  on  the  ventral  surface  of  the 
body-cavity.  These  ganglia  are  centers  for  movements  and 
respiration  in  the  somites  to  which  they  belong. 


THE   COMMON  RED-LEGGED  LOCUST 


11 


The  Muscular  System.  All  the  muscles  of  the  body  are 
supplied  with  microscopic  nerves.  The  muscles  are  attached 
to  the  hard  covering  of  the  body,  and  when  stimulated  by 
the  nervous  system  they  contract,  thus  moving  the  part  to 
which  they  are  attached.  Though  delicate  in  appearance  the 
muscles  are  in  reality  very  strong,  as  may  be  understood 
when  the  activity  of  the  insect  is  considered. 

The  Reproductive  System.  As  in  most  other  animals,  the 
union  of  two  dissimilar  elements  is  necessary  for  the  produc- 
tion of  a  new  locust.  These  elements  are  the  very  small, 
active  sperm-cells  produced  by  the  male,  and  the  larger,  pas- 
sive egg-cell  produced  by  the  female.  On  the  union  of  these 
two  cells  the  egg-cell  is  said  to  be  fertilized  and  the  growth 
of  a  new  individual  is  begun.  Occupying  a  considerable  part 
of  the  posterior  portion  of  the  abdomen  of  the  female  are  the 
ovaries  (Fig.  3,  30,  31),  two  sets  of  delicate  tubular  organs  in 
which  the  egg-cells  are  developed.  These  are  connected  with 
the  surface  by  the  egg-tube,  or  oviduct  (Fig.  3,  32).  In  the 
male  the  sperm-cells  are  secreted  in  glands  called  spermaries, 


FIG.  4.   Rocky  Mountain  Locust  Laying  Eggs.    About  natural  size. 
(After  Riley) 

A,  B,  female  laying  eggs  ;  C,  diagram  showing  the  arrangement  of  eggs  in  the  hole ; 
JJ,  mass  of  eggs  removed  from  hole  and  part  of  covering  taken  away ;  E,  few 
eggs  separated 


12 


GENERAL   ZOOLOGY 


FIG.  5.   Development  of  Locust 


A,  P>,  C,  D,  E,  F,  stages  from  nymph  to  adult, 
enlarged:  A  X  6,  B  x  2,  the  others  slightly 
enlarged 
(From  Packard's  Text-Book  of  Entomology') 


which  form  a  tubular  mass  in  the 
third,  fourth,  and  fifth  abdominal 
somites.  After  fertilization  the 
eggs  are  covered  on  the  way  down 
the  egg-tube  by  a  sticky  substance 
poured  out  from  the  cement  or 
colleterial  gland  (Fig.  3,  33).  This 
gland  opens  into  a  capacious 
pouch  (bursa  copulatrix,  Fig.  3,  34), 
which  rests  on  and  opens  directly 
into  the  oviduct. 

Development.    The  eggs  of  the 
red-legged  locust  are  laid  in  the 
autumn  in  holes  made  by  the 
ovipositor  of  the   female,  in 
the  ground  of  fields,  pastures, 
and  waysides.    They  differ  in 
no  important  respect  from  the 
eggs  of  the  Rocky  Mountain 
locust  shown  in  Fig.  4.  Each 
hole  contains  from  twenty  to 
thirty-five  eggs.    A  secretion 
from  the  gland  already  men- 
tioned binds  all  the  eggs  in  a 
single    hole   into    one 
mass,    and    when    the 
number  is  completed 
more    fluid    is    poured 
out,  which  hardens  into 
a  firm  covering.    Here 
they   remain    over   the 
winter  and   hatch   out 
into   young  locusts  in 
the  spring,  quite  closely 


THE  COMMON  RED-LEGGED  LOCUST 


13 


resembling  the  adult 
except  in  absolute 
and  relative  size  of 
parts  and  in  the  ab- 
sence of  wings.  They 
grow  rapidly,  molting 
several  times  during 
the  summer,  appear- 
ing  each  time  a  little 
larger  and  with  more 
fully  developed  wings. 
While  these  changes 
are  going  on  the  young 
locust  is  called  a 
nympli  (Fig.  5,  A—E). 
When  ready  for  the 
last  molt,  which  takes 
place  late  in  the 
summer,  the  nymph 
climbs  up  some  grass 
stem  or  similar  ob- 
ject, and,  taking  firm 
hold,  often  with  its 
head  pointing  down- 
ward, remains  mo- 
tionless for  several 
hours,  till  the  skin 
swells  over  the  head 
and  thorax  and  finally 
splits  open  along  a 
median  dorsal  line. 
From  this  old  skin 
the  new  head,  tho- 
rax, legs,  wings,  and 


FIG.  6.   The  Molting  of  Locust.    Slightly 

enlarged.    (After  Riley) 

A,  13,  C,  D,  E,  successive  stages  in  the  process 
of  molting 


14  GENERAL   ZOOLOGY 

abdomen  are  slowly  withdrawn  while  soft,  expanding  and 
hardening  within  half  or  three  quarters  of  an  hour  (Fig.  6). 
It  is  now  a  perfect  insect,  or  imago,  of  full  size  and  with  fully 
developed  wings.  After  the  females  have  laid  their  eggs  in 
the  fall  most  of  the  locusts  die. 

Relation  to  Environment.  Red-legged  locusts  are  found  in 
meadows,  pastures,  fields,  and  along  roadsides,  though  most 
abundant  where  the  vegetation  is  succulent.  Specimens  from 
low,  damp  ground  are  usually  somewhat  darker  in  color  than 
those  from  high,  dry  areas.  Their  food  consists  of  the  leaves 
of  grasses  and  other  vegetation.  The  strength  of  the  man- 
dibles and  the  complexity  of  the  digestive  system  fit  them 
admirably  for  a  life  of  constant  forage.  Their  color  is,  to  a 
certain  extent,  protective,  for  they  are  not  easily  seen  among 
the  dried  grasses  of  the  summer. 

Locusts  have,  when  adult,  a  choice  of  three  methods  of 
progression, — walking,  jumping,  and  flying.  The  many  spines 
pointing  downward  on  the  legs  and  the  pulvilli  between  the 
tarsal  claws  make  climbing  an  easy  matter.  The  complicated 
system  of  air-sacs  tends  to  reduce  the  weight  of  the  body  in 
flight.  By  means  of  the  air-sacs  and  wings  the  locust  has 
solved  the  problem  of  aerial  locomotion. 

The  list  of  the  locust's  enemies  is  long  and  formidable, 
even  if  man  is  not  considered.  Small  animals,  such  as  moles 
and  birds,  especially  the  crow  and  blackbird,  feed  on  the 
eggs  and  young.  Some  species  of  wasps  use  the  nymphs  to 
provision  their  nests,  first  stinging  them  to  render  them  help- 
less. They  are  also  subject  to  a  disease  caused  by  a  fungous 
growth,  and  may  often  be  found  firmly  attached  to  some  grass- 
blade  to  which  they  have  clung  before  death.  That  they  have 
been  able  to  maintain  themselves  in  such  large  numbers  in 
spite  of  all  their  enemies  marks  them  as  successful  competitors 
in  the  struggle  for  existence. 


CHAPTER  II 

'^--:-r 

THE  ALLIES  OF  THE  RED-LEGGED  LOCUST :  ORTHOPTERA 

The  poetry  of  nature  is  never  dead  : 

When  all  the  birds  are  faint  with  the  hot  sun, 

And  hide  in  cooling  trees,  a  voice  will  run 

From  hedge  to  hedge  about  the  new-mown  mead : 

That  is  the  grasshopper's,  —  he  takes  the  lead 

In  summer  luxury,  —  he  has  never  done 

With  his  delights.  —  KEATS. 

Locusts.  Though  the  common  red-legged  locust  is  widely 
distributed  throughout  the  United  States,  it  has  not  attracted 
so  much  attention  as  the  Rocky  Mountain  locust,  for  its 
effects  on  agriculture  have  not  been  so  marked.  The  latter 
has  the  remarkable  habit  of  migrating  from  its  habitat  (see 
map,  p.  17)  on  the  dry  plains  east  of  the  Rocky  Mountains, 
destroying  in  a  few  hours  the  labors  of  the  farmer  for  several 
months.  Not  only  are  growing  crops  devoured,  but  every 
green  thing  is  attacked,  leaving  the  country  as  bare  as  if  a 
fire  had  swept  over  it.  It  has  been  said  that 'these  swarms 
occur  at  intervals  of  about  eleven  years.  The  locusts  show  a 
tendency  to  become  gregarious  (having  the  habit  of  associat- 
ing in  groups)  from  the  beginning  of  their  life  as  nymphs, 
but  their  migrations  are  not  generally  begun  before  they  are 
at  least  half  grown.  These  hordes  proved  so  destructive  to 
the  agricultural  district  of  the  Middle  West  from  1873  to 
1877  that  a  commission  was  appointed  by  the  government 
to  study  their  habits  and  to  report  upon  ways  and  means  for 
checking  their  devastations.  Of  late  years  this  species  has 
not  been  so  abundant  or  so  destructive.  Many  machines  have 
been  constructed  to  capture  them.  A  recent  method  of  fight- 
ing them  is  to  cultivate  in  a  sweet  solution  a  fungous  growth 

15 


16  GENERAL   ZOOLOGY 

which  destroys  them.  Members  of  the  swarm  are  then  cap- 
tured, dipped  in  the  solution,  and  turned  loose,  thus  spreading 
the  disease.  The  lesser  locust  has  at  various  times  caused  con- 
siderable damage  to  growing  crops  by  appearing  at  different 
points  in  the  New  England  states. 

There  are  several  species  of  migratory  locusts  in  the  Old 
World  whose  visitations  in  the  past  have  been  most  destruc- 
tive, especially  in  Egypt,  Palestine,  Syria,  Asia  Minor,  China, 
France,  Russia,  and  Germany.  They  have  appeared  in  almost 
incredible  numbers  in  certain  years,  so  that  a  swarm  has  been 
estimated  to  cover  two  thousand  square  miles  of  territory. 
The  prophet  Joel  has  described  the  onslaught  of  locusts  in 
the  lines  beginning,  — 

A  day  of  darkness  and  of  gloominess,  a  day  of  clouds  and  of  thick  dark- 
ness, as  the  morning  spread  upon  the  mountains :  a  great  people  and  a 
strong;  there  hath  not  been  ever  the  like,  neither  shall  be  any  more  after 
it,  even  to  the  years  of  many  generations.  — JOEL  ir :  2. 

It  is  easy  to  appreciate  the  fact  that  in  thickly  settled  areas 
famine  and  pestilence  may  follow  the  visitation  of  these  in- 
sects. Out  of  the  twelve  hundred  or  fifteen  hundred  species 
of  locusts  in  the  world,  only  about  twelve  have  the  habit  of 
migration  to  any  great  extent,  and  these  are  mostly  species 
which  live  on  large,  elevated,  open  tracts  of  desert  or  semi- 
desert  character,  where  the  climate  is  dry  and  hot,  —  for  ex- 
ample, such  regions  as  the  steppes  about  the  Caspian  Sea. 
Perhaps  the  determining  factor  in  the  migration  is  exces- 
sive multiplication  and  the  consequent  need  for  new  feeding- 
ground. 

Many  locusts  produce  sounds  by  rubbing  the  inner  edge 
of  the  posterior  femur  against  the  outer  edge  of  the  first  pair 
of  wings.  It  is  supposed  that  this  is  done  only  by  the  males, 
though  it  may  be  possible  that  the  females  produce  sounds 
which  we  are  unable  to  hear.  Some  locusts  produce  a  noise 
in  flight  by  the  friction  of  the  wings. 


17 


18  GENERAL   ZOOLOGY 

Locusts  have  been  and  are  used  to-day  as  food  in  various 
parts  of  the  East.  The  records  on  the  bricks  of  Babylon  and 
Nineveh  show  that  they  were  known  in  early  times  as  food, 
and  they  are  mentioned  among  the  clean  meats  in  Leviticus 
xi.  22.  They  are  in  common  use  among  the  Arabs  and  the 
Bushmen ;  our  own  Rocky  Mountain  locust  has  been  eaten 
and  pronounced  quite  palatable. 

Grasshoppers.  The  insects  which  so  far  we  have  been  con- 
sidering, while  often  spoken  of  as  grasshoppers,  are  not  true 


FIG.  8.    Katydid.    Natural  size 
(From  Hunter's  Studies  in  Insect  Life) 

grasshoppers,  though  closely  allied  to  them.  The  locusts 
have  short,  rather  stout,  antennre,  while  the  true  grasshoppers 
have  thread-like  antennae,  much  longer  than  the  body.  Per- 
haps the  most  interesting  of  the  grasshoppers  are  the  katy- 
dids (Fig.  8),  large  green  insects  of  arboreal  (tree-dwelling) 
habits,  found  in  the  eastern  and  central  United  States. 
They  afford  an  illustration  of  protective  resemblance,  —  a  term 
which  is  used  to  cover  those  cases  in  which  an  animal  pos- 
sesses colors  or  shape  which  harmonize  with  its  environment 
(surroundings),  or  with  some  particular  object  in  the  environ- 
ment, thus  affording  protection  against  enemies.  In  the  case 
of  katydids  the  whole  body  is  green  and  the  wings  are  thin 
and  veined  like  a  leaf.  The  well-known  note  from  which  the 
name  "  katydid  "  is  derived  is  produced  only  by  the  male,  and 


THE  ALLIES   OF  THE  EED-LEGGED  LOCUST     19 

is  made  by  rubbing  the  base  of  one  of  the  first  pair  of  wings 
against  the  other  anterior  wing.  An  auditory  apparatus  is 
found  in  both  sexes  at  the  base  of  the  front  tibise. 

Some  of  the  grasshoppers  have  taken  to  a  cave  life,  and  are 
blind  and  wingless.  Color  has  not  been  developed,  and  the 
insects  have  the  white  appearance  of  plants  grown  in  the 
dark.  The  antennae  and  legs  are  elongated  to  an  enormous 
extent,  and  must  be  useful  in  an  environment  where  much 
depends  on  the  sense  of  touch. 

Crickets.  The  crickets  (Fig.  9,  A)  resemble  the  grasshop- 
pers in  the  possession  of  long,  slender  antennae,  but  differ 
from  them  in  having  the  anterior  wings  overlapping,  instead 
of  meeting  in  a  ridge  along  the  median  line  of  the  back. 
They  are  widely  distributed  over  the  earth,  and  are,  as  a 


FIG.  9.    Cricket 

A,  female,  natural  size.  J5,  under  surface  of  right  wing  of  male,  enlarged :  1,  rasp ; 
2,  position  of  scraper,  only  the  scraper  of  left  wing  used ;  3,  attachment  of  wing 

rule,  nocturnal  in  their  habits.  They  feed  mostly  on  vege- 
table matter.  Our  native  species  live  in  the  fields  beneath 
sticks  and  stones.  Of  late  years  the  house-cricket  of  Europe 
(Gryl'lus  domes' tieus)  has  become  common  in  the  cities  of  the 
eastern  United  States.  This  is  the  species  famous  in  song 
and  story.  Its  well-known  chirp  is  made  only  by  the  male. 
The  principal  vein  on  the  ventral  surface  of  each  anterior  wing 
is  thickened  into  a  rasp-like  structure  (Fig.  9,  B,  1) ;  on  another 


20  GENERAL   ZOOLOGY 

part  is  a  hardened  portion  called  the  scraper  (Fig.  9,  B,  2).  The 
noise  is  produced  by  raising  the  anterior  wings  and  rubbing  the 
rasp  of  the  right  wing  against  the  scraper  of  the  left.  Fig.  9 

shows  one  of  the 
species  common 
in  the  eastern 
United  States. 

The  mole-crick- 
ets ( Grryllotalf/pa. 
FIG.  10.   Mole-Cricket.     Slightly  enlarged  „. 

tig.  10)  are  bur- 
rowing insects,  which  show  interesting  adaptations  to  sub- 
terranean life.  The  fore  legs  are  thickened  and  adapted  to 
burrowing.  Roots  are  easily  cut  in  two  by  means  of  a  shear- 
like  motion  of  the  joints  of  each  front  tarsus  against  the 
teeth  of  the  tibia  of  that  leg.  For  this  reason  mole-crickets, 
when  numerous,  are  sometimes  a  serious  pest.  The  female 
mole-cricket  watches  over  her  eggs  and,  when  they  are  hatched, 
feeds  the  young  till  the  first  molt.  Mole-crickets  are  found 
both  in  America  and  Europe. 

Cockroaches.  The  cockroaches  are  cosmopolitan  forms, 
some  of  which  infest  our  houses,  where  they  feed  on  both 
animal  and  vegetable  matter.  They  are  dark-colored,  flattened 
insects,  which  depend  upon  their  legs  for  escape,  although 
most  of  them  possess  wings.  Their  flattened  bodies  make  it 
easy  for  them  to  hide  in  crevices,  whence  they  come  out  at 
night  to  feed.  The  female  carries  her  eggs  about  with  her 
in  a  large  case  till  the  young  are  nearly  ready  to  appear. 
It  has  been  asserted  of  some  species  that  the  mother  assists 
the  young  in  escaping  from  the  egg-case.  Just  before  hatch- 
ing, the  distance  between  the  lateral  surfaces  of  the  young 
cockroach  is  only  one  third  of  the  diameter  from  the  dorsal 
to  the  ventral  surface.  Soon  after  hatching,  it  assumes  the 
dorso-ventral  flattened  form  of  the  adult,  —  an  adaptation  to 
their  life  in  concealed  places.  Fig.  11  shows  the  German 


THE  ALLIES   OF  THE  KED-LEGGED  LOCUST      21 

cockroach,  or  "croton-bug"  (Phyllodro'mia  german'icd),  with 
its  egg-case ;  and  a  larger  species,  the  so-called  Oriental 
cockroach  (Stiloyjyga  orien'talis),  though  there  is  little  evi- 
dence to  show  its  original  home. 

Walking-Sticks.  The  peculiar  insects  called  walking-sticks 
are  also  related  to  the  locusts.  Among  them  are  some  of 
the  most  remarkable  illustrations  of  protective  resemblance 
known  in  the  animal  kingdom.  The  common  species  in  the 
eastern  United  States  (Diapherom1 'era  femora' to)  is  shown 
in  Fig.  12.  The  body  and  legs  are  elongated  to  such  an 
extent  that  when  at  rest  the  resemblance  to  a  twig  is  most 


FIG.  11.   Cockroaches.    Natural  size 


striking.  The  insect  undergoes  a  seasonal  change  of  color, 
being  brown  when  first  hatched,  turning  green  after  feeding, 
and  changing  to  brown  again  as  the  season  advances.  It  has 
the  power  of  replacing  broken  appendages  at  the  next  molt, 


22 


GENERAL   ZOOLOGY 


the  portion  reappearing  either  as  a  short  stump  or  as  a 
smaller  appendage,  complete  except  for  the  absence  of  one 
tarsal  joint.  This  walking-stick  is  a  voracious  feeder  on  the 
leaves  of  trees ;  it  has  been  known  to  eat  a  piece  of  leaf  an 
inch  long  and  a  third  of  an  inch  wide  in  an  hour. 

Closely  related  to  the  walking-sticks  are  the  peculiar  East 
Indian  insects  known  as  walking-leaves.  In  these  insects 
the  anterior  wings  of  the  female  are  green  and  veined  like  a 

leaf.  The  people  in 
the  countries  where 
they  are  found  be- 
lieve that  these 
insects  are  really 
transformed  leaves. 
The  males  are  en- 
tirely different  from 
the  females,  having 
anterior  wings 
which  have  no  leaf- 
like  appearance. 

Mantids.  The 
^  mantids  are  remark- 
able for  the  de- 
velopment of  the 
fore  legs,  which 
are  unusually  large 
and  strong  and 
armed  with  stout 
spines.  The  func- 
tion of  these  legs  is 

to  seize  and  hold  living  prey,  which  consists  of  other  insects. 
When  lying  in  wait  the  fore  legs  are  held  up  in  the  air, 
but  when  an  insect  comes  within  reach  they  are  extended 
with  swiftness  and  precision.  The  eggs  of  the  mantids  are 


FIG.  12.   Walking-Stick,     x  f 


THE  ALLIES   OF  THE  RED-LEGGED  LOCUST      23 

deposited  in  a  mass  of  foam-like  matter,  which  the  female 
discharges  from  the  tip  of  the  abdomen.  This  material  soon 
hardens  and  forms  a  protecting  case  for  the  eggs.  The  mantid 


FIG.  13.   Japanese  Mantid.    Natural  size 

shown  with  /  I  its  egg-case  in  Fig.  13  is  a  Japanese  species 
(Tinode'ra  sinen'sis),  which  has  recently  been  intro- 

duced  in   a  few  places  in  the  eastern  United  States. 

The  color  is  brown  and  is  to  some  extent  protective,  and 

as  this  inconspicuous  coloration  may  render  it  easier  for  the  in- 
sect to  approach  its  prey  or  to  escape  notice  while  waiting  for 
food,  it  may  be  classed  as  an  example  of  aggressive  resemblance, 
which  term  covers  those  cases  where  an  animal,  in  resembling 
its  immediate  environment,  either  in  shape  or  color,  or  both, 
is  thought  thereby  to  be  assisted  in  attack  on  its  prey. 

Several  species  of  mantids  from  India  resemble  different 
flowers  which  are  visited  by  insects,  and  seize  upon   such 


24  GENERAL   ZOOLOGY 

unwary  visitors  as  do  not  detect  the  imposition.  In  this  case 
the  resemblance  is  to  an  object  attractive  to  the  prey,  and 
may  be  spoken  of  as  alluring  coloration.  Dr.  J.  Anderson 
showed  specimens  of  one  of  these  insects  to  members  of  the 
Asiatic  Society  of  Bengal  in  1877,  and  communicated  infor- 
mation concerning  them  as  follows.  "  On  looking  at  the 
insects  from  above,  they  did  not  exhibit  any  very  striking 
features  beyond  the  leaf-like  expansion  of  the  prothorax  and 
the  foliaceous  appendages  to  the  limbs,  both  of  which,  like 
the  upper  surface  of  the  insect,  are  colored  green ;  but  on 
turning  to  the  under  surface  the  aspect  is  entirely  different. 
The  leaf-like  expansion  of  the  prothorax,  instead  of  being 
green,  is  a  clear,  pale  lavender  violet,  with  a  faint  pink  bloom 
along  the  edges  of  the  leaf,  so  that  a  portion  of  the  insect 
has  the  exact  appearance  of  the  corolla  of  a  plant,  —  a  floral 
simulation  which  is  perfected  by  the  presence  of  a  dark,  black- 
ish-brown spot  in  the  center  over  the  prothorax,  and  which 
mimics  the  opening  to  the  tube  of  a  corolla.  A  favorite  posi- 
tion of  this  insect  is  to  hang  head  downwards  among  a  mass 
of  green  foliage ;  and  when  it  does  so  it  generally  remains 
almost  motionless,  but  at  intervals  evinces  a  swaying  move- 
ment, as  of  a  flower  touched  by  a  gentle  breeze." 

Definition  of  Orthoptera  (Gr.  orthos,  straight;  pteron,  wing). 
All  the  insects  mentioned  in  this  chapter  have  the  mouth-parts 
adapted  to  biting,  and  most  of  them  have  two  pairs  of  wings. 
The  posterior  wings,  when  present,  are  folded  lengthwise  like 
a  fan  beneath  the  hardened  anterior  wings,  and  are  thus  pro- 
tected from  injury.  These  insects  agree  in  their  mode  of 
growth,  which  is  a  gradual  increase  of  size  by  successive  molts, 
without  any  abrupt  change  of  form.  The  imagoes  differ  from 
the  nymphs  chiefly  by  their  larger  size  and  the  presence  of  wings. 
On  account  of  these  common  characteristics  these  insects  are 
united  in  a  group,  or  order,  called  Ortliop' tera,  in  allusion  to 
the  longitudinal  folding  of  the  posterior  pair  of  wings. 


CHAPTER   III 

THE    MAY-FLIES  (PLECTOPTERA)  AND  THE   DRAGON- 
FLIES  (ODONATA) 

The  sun  comes  forth  and  many  reptiles  spawn  ; 

He  sets  and  each  ephemeral  insect  then 

Is  gathered  into  death  without  a  dawn, 

And  the  immortal  stars  awake  again.  — SHELLEY. 

May-Flies.  The  May-flies  (Fig.  14),  which  stand  in  litera- 
ture as  the  type  of  brief  and  purposeless  existence,  are  deli- 
cately constructed,  pale  insects,  with  usually  four  finely 
veined  wings  and  two  or  three  long  white  filaments  project- 
ing from  the  end  of  the  abdomen.  The  eyes  are  compara- 
tively large,  but  the  mouth-parts  are  so  reduced  that  no  food 
can  be  taken  during  adult  life,  which  in  most  species  lasts 
only  a  few  hours.  May-flies  appear  in  countless  numbers  in 
late  spring  or  early  summer,  dance  about  in  the  air  at  dusk 
in  swarms  so  dense  that  the  atmosphere  seems  one  mass  of 
moving  forms,  and,  after  laying  their  eggs,  perish  with  the 
day,  forming  a  great  food-supply  for  fishes  and  birds. 

The  eggs  are  laid  in  the  water  and  hatch  into  nymphs 
(Ephem'era,  Fig.  14),  which  do  not  at  all  resemble  the  adult, 
and  are  adapted  to  an  aquatic  existence  by  the  presence,  along 
the  sides  of  the  abdomen,  of  outgrowths  of  the  body-wall  pene- 
trated by  tracheae.  These  outgrowths  are  called  tracheal  gills. 
The  delicate  skin  of  which  the  gills  are  formed  permits  the 
passage  of  oxygen  from  the  surrounding  water  inward,  and 
allows  the  escape  of  carbon  dioxide  gas.  The  posterior  divi- 
sion of  the  heart  (or  an  accessory  chamber)  is  so  arranged, 
that  it  propels  blood  backward  into  the  abdominal  filaments, 
so  that  they,  too,  act  as  an  organ  of  respiration.  The  young 

25 


GENERAL   ZOOLOGY 


feed  on  small  aquatic  animals,  or  on  plants.  After  a  year  or 
more  of  this  life  beneath  the  surface,  during  that  time  under- 
going many  molts,  the  nymph  de- 
velops rudimentary  wings.  From 
the  nymph  issues  a  winged  form 
which  may  be  called  a  subimago. 
Within  a  very  short  time  the  skin 
is  again  cast,  even  to  a  thin  cover- 
ing from  the  wings,  and  the  true 
imago  comes  forth.  A  molt  in  the 
winged  state  is  known  nowhere 
else  among  insects.  Though  the 
reduced  mouth-parts  make  it  im- 
possible for  the  adult  May-fly 
to  take  any  food,  the  alimen- 
tary canal  is  not  useless.  Air  is 


FIG.  14.   Nymph  and  Imago  of  May-Fly.    Natural  size 

taken  in  at  the  mouth,  and  the  capacious  stomach  acts  as  a  bal- 
loon, being  provided  with  valves  so  that  the  air  cannot  escape. 
Definition  of  Plectoptera  (Gr.  plektos*  twisted:  pteron* 
wing).  The  May-flies  make  up  the  order  Plectop'tera.  The 
Plectoptera  may  be  distinguished  from  other  insects  by  the 
reduced  mouth-parts,  the  great  disproportion  in  the  size  of 


THE  MAY-FLIES  AND  THE  DRAGON-FLIES       27 

the  anterior  and  posterior  wings,  and  by  the  presence  of 
abdominal  filaments.  From  the  earliest  nymph  stage  to  the 
imago  there  is  quite  a  clearly  marked  though  gradual  change 
of  form,  or  metamorphosis. 

To-day  I  saw  the  dragon-fly 

Come  from  the  wells  where  he  did  lie. 

An  inner  impulse  rent  the  veil 

Of  his  old  husk  :  from  head  to  tail 

Came  out  clear  plates  of  sapphire  mail. 

He  dried  his  wings  :  like  gauze  they  grew ; 

Thro'  crofts  and  pastures  wet  with  dew 

A  living  flash  of  light  he  flew.  — TENNYSON. 

Dragon-Flies.  The  dragon-flies  (Libel'lula,  Fig.  15)  are 
familiar  insects  found  flying  over  the  surface  of  still  or  run- 
ning water.  They  feed  on  other  insects,  which  they  capture 
on  the  wing.  They  are  lovers  of  the  sunshine,  and  are  most 
active  in  the  brightest  and  hottest  part  of  the  day.  The  larger 
kinds  hawk  freely  over  the  surface  of  the  water  at  some  dis- 
tance above  it,  often  far  out  from  the  shore,  where  their  range 
of  vision  is  unobstructed  ;  while  the  smaller  and  weaker  kinds 
keep  closer  to  the  shore  and  the  protection  of  vegetation.  All 
are  voracious  feeders,  destroying  large  quantities  of  flies  and 
mosquitoes.  Many  superstitions  have  become  associated  with 
them  in  different  parts  of  the  country ;  in  the  North  it  is 
believed  that  they  sew  up  the  mouths  and  ears  of  children ; 
in  the  South,  that  they  bring  dead  snakes  to  life.  It  is,  per- 
haps, needless  to  say  that  they  are  harmless.  The  head  is 
made  up  almost  entirely  of  the  great,  staring,  compound 
eyes,  which  shine  like  fire  as  the  dragon-fly  moves  about. 
The  mouth  has  strong  jaws,  somewhat  resembling  the  power- 
ful mandibles  of  the  locusts.  The  wings  are  large,  with 
many  veins,  and  are  moved  by  powerful  muscles  ;  but  the  legs 
are  slender  and  small,  as  the  dragon-flies  are  preeminently 
creatures  of  the  air.  The  long  and  slender  abdomen  is  used 
to  balance  the  insect  in  its  headlong  flight. 


28 


GENERAL  ZOOLOGY 


it 


The  eggs,  generally  attached  to  water  plants,  hatch  into 
dark-colored,  flattened  aquatic  nymphs.  The  mouth-parts 
are  unique  in  structure.  The  second  maxillae  are  enlarged 
and  armed  with  hooks  at  the  extremity.  This  formidable 

organ  can  be  extended  to  seize 
upon  any  insect  within  reach,  and 
when  not  so  engaged  it  covers 
the  entire  face  like  a  mask,  giv- 
ing a  peculiar  and  comical  aspect 
to  a  front  view.  The  nymphs 
breathe  by  means  of  tracheae, 
which  line  the  posterior  portion 
of  the  alimentary  canal.  When 
water  is  drawn  into  the  canal, 
air  is  absorbed  from  it  by  this 


FIG.  15.    Metamorphosis  of  Dragon-Fly.    Natural  size 


THE  MAY-FLIES  AND  THE  DRAGON-FLIES      29 

system  of  air-tubes,  and  water,  deprived  of  its  free  oxygen, 
can  be  ejected  violently,  thus  forcing  the  nymph  forward. 
After  successive  molts  the  nymph  develops  rudiments  of 
wings,  and  finally  crawls  out  of  the  water  to  some  conven- 
ient support,  when  the  skin  splits  down  the  back  and  the 
dragon-fly,  with  crumpled  wings,  slowly  emerges.  A  short 
time  elapses  before  the  body  hardens  and  the  wings  expand, 
and  then  the  imago  flies  away  to  live  its  short  adult  life. 

There  are  two  quite  distinct  types  of  dragon-flies,  both 
widely  distributed  over  the  world.  The  form  represented  in 
Fig.  15  is  of  comparatively  robust  build.  The  eyes  touch 
each  other  along  the  median  line  of  the  head.  The  posterior 
wings  are  broader  at  the  base  than  the  anterior  pair,  and  both 
pairs  are  held  horizontally  when  the  insect  is  at  rest.  To  this 
type  belong  the  best  fliers  of  the  group.  The  insects  which 
illustrate  the  other  type,  while  they  can  easily  enough  be 
recognized  as  dragon-flies,  are  of  more  slender  build.  Their 
eyes  are  widely  separated  on  opposite  sides  of  the  head.  The 
anterior  and  posterior  wings  are  alike  in  size  and  shape,  and 
when  not  in  use  are  folded  against  the  abdomen.  The  flight 
is  less  sustained  and  more  erratic  than  with  species  of  the 
first  type.  Some  of  these  dragon-flies,  notably  species  from 
the  tropics,  are  most  beautiful  both  in  form  and  color.  The 
French  call  these  insects  "  demoiselles,"  which  we  may  trans- 
late damsel-flies. 

Definition  of  Odonata  (Gr.  odons  (odont],  a  tooth).  The 
dragon-flies  constitute  the  order  Odona'ta,  a  word  meaning 
"  toothed,"  perhaps  in  allusion  to  the  teeth  on  the  second 
maxillae  of  the  larvae.  The  Odonata  are  distinguished  by  the 
biting  mouth-parts  and  the  four  equal  or  nearly  equal  net- 
veined  wings.  The  metamorphosis  is  fully  as  well  marked 
as  in  the  preceding  order. 


CHAPTER  IV 


THE  BUGS:   HEMIPTERA 

The  shy  cicada,  whose  noon-voice  rings 
So  piercing  shrill  that  it  almost  stings 

The  sense  of  hearing.  — ELIZABETH  A.  KERR. 

Water-Bugs.    In  almost  every  pond  and  stream,  not  only 
in  the  United  States  but  scattered  widely  over  almost  the 

whole  world,  are  to  be  found 
oval  gray  and  black  insects, 
usually  a  little  over  a  ceri- 
^^_    timeter  long  (about  half  an 
inch).   These  are  water-boat- 
men (Corix'a,  Fig.  16,  B).     They  have 
a  long  beak  formed  by  the  union  and 
lengthening    of    the    second    maxilla}, 
inclosing    at   its   base   the    bristle-like 
mandibles    and    first    maxillae.      With 
this  they  suck  the  body -fluids  of  other 
water-creatures.     They  are  adapted  to 
rapid  locomotion  in  the  water  by  means 
of  the  lengthened  and  fringed  middle 
and   hind  legs.     They  breathe   a  thin 
film  of  air,  which  is  caught  in  the  fine 
hairs   which   cover  the  body,   making 
them  look  as  if  .  incased   in  polished 
metal.    Slight  movements  of  the  legs 
cause  currents  of  water  to  pass  over 
this  air-film,  helping  to  purify  it,  and 
rendering  frequent  visits  to  the  surface 
unnecessary.    When  at  the  surface  air 
30 


FIG.  16.  Back -Swimmers 
and  Water-Boatman. 
Slightly  enlarged 

A,  Notonecta,  ventral  view 
-(swimming  attitude); 
A',  Notonecta,  dorsal  sur- 
face ;  B,  Corixa 


THE  BUGS:    HEMIPTERA 


31 


is  taken  into  a  cavity  under  the  wings,  where  the  spiracles 
are  placed,  so  that  quite  a  supply  is  on  hand  at  all  times. 
While  these  insects  are  thus  adapted  to  water-life,  they  can 
fly,  and  often  leave  their  native  ele- 
ment, especially  if  it  is  in  danger 
of  becoming  dry. 

Another    widely   distributed 
group   of   insects   resembling    the 
foregoing  are  the  back-swimmers 
(Notonec'ta,  Fig.  16, 
A,  A'),  which  have 
the   curious   habit   '• 
of    swimming    on 
their   backs,   as 
their  common  arid  scientific 
names  denote.    A  favorite  posi- 
tion of  these  insects  is  to  float  with  the 
head  down  and  the  tip  of  the  abdomen 
protruding  just  enough    to   admit   the 
passage  of  air  to  chambers  beneath  the 
wing-covers.     The    back-swimmers    can 
inflict    a    momentarily    painful    wound 

with  their  sharp  beaks.     Search  made 

.  .  FIG.  17.   Squash-Bug  and 

for  these  insects  will  reveal  a  variety  of      Young.    Natural  size 

other  beaked  forms,  some  of  which  live 

beneath  the  surface  of  water,  while  others  skim  swiftly  over  it. 
Plant-Bugs.  The  squash-bug  (An'asa  tris'tis,  Fig.  17),  a 
well-known  enemy  of  squash  and  pumpkin  vines,  also  pos- 
sesses a  beak,  which  is  used  to  suck  plant  instead  of  animal 
fluids.  This  bug  is  a  little  over  two  centimeters  (nearly  an 
inch)  long,  and  brownish  black  in  color.  It  has  the  power, 
in  common  with  many  other  allied  species,  of  pouring  out  an 
evil-smelling  secretion  from  two  openings  near  the  base  of 
the  middle  pair  of  legs,  which  probably  renders  it  obnoxious 


32 


GENERAL  ZOOLOGY 


to  some  creatures  which  might  prey  upon  it.    Observations 
on  the  food  of  birds  of  the  eastern  United  States  seem  to 
dpi         show  that,  so  far  at  least  as  the  birds  are  con- 
cerned, these  repellent  odors  are  not  in  all  cases 
entirely  effective,  since  many  species  of  plant- 
bugs  are  fed  upon  quite  generally  by  birds. 

Cicadas.   An  examination  of  the  large,  broad- 
headed,  triangular  insects  known  as  harvest- 
flies,  or  cicadas,  will  show  that  they,  too,  agree 
with  the  foregoing  insects   in  the   possession 
of  a  sucking-beak.    There  are  several  species 
in  the   United  States,  of  which  the  best 
known  is  the  periodical  cicada  (Cica'da 
septen'decim,  Fig.  18),  usually,  but  wrong- 
ly, called  the  thirteen  or  seventeen  year 
"  locust.1'    At  the  base  of  the  abdomen  of 
the  male  is  a  "  drum," 
or  sound-producing 
organ,  where  a  high- 
pitched  note  is  made 
by  the  rapid 


FIG.  18.    Periodical  Cicada,     x 


THE  BUGS:    HEMIPTERA  33 

vibration  of  tightly  stretched  membranes,  somewhat  in  the 
way  sound  may  be  produced  by  pushing  up  and  down  on 
the  bottom  of  a  tin  pan.  This  note,  heard  in  the  middle  of 
hot  summer  days,  has  been  celebrated  as  the  "song"  of  the 
cicada  since  the  time  of  the  Greeks. 

The  female  lays  her  eggs  in  slits,  usually  in  the  small 
terminal  twigs  of  trees,  generally  causing  them  to  wither 
and  die.  In  a  year  in  which  these  insects  appear  in  large 
numbers  the  trees  look  as  if  a  fire  had  passed  over  them 
and  scorched  the  ends  of  all  the  twigs.  The  eggs  hatch  in 
about  six  weeks,  and  the  nymphs  drop  to  the  ground,  into 
which  they  dig,  and  for  a  long  period  of  time,  thirteen  years 
in  the  southern  states  and  seventeen  years  in  the  North, 
they  lie  in  a  cell  feeding  on  the  juices  of  the  roots  of  trees. 
Early  in  the  summer  of  the  thirteenth  or  seventeenth  year, 
they  rise  to  the  surface,  and,  clinging  to  some  convenient 
support,  cast  their  last  nymph  skin  to  come  out  as  winged 
creatures  for  their  few  weeks  of  adult  life.  In  some  cases, 
when  the  nymphs  reach  the  surface,  they  build  peculiar 
cones  of  clay  (Fig.  18)  several  inches  in  height,  over  the 
mouths  of  their  burrow's,  entirely  closing  the  top  of  the 
cone.  In  the  upper  part  of  these  they  wait  the  period  of 
their  final  molt.  The  formation  of  these  structures  has  been 
explained  by  some  as  due  to  the  prevalence  of  long-continued 
wet  weather  at  the  time  of  the  emergence ;  by  others,  as 
occasioned  by  heating  of  the  ground  in  certain  localities  by 
the  sun,  thus  bringing  the  nymphs  to  the  surface  before  their 
time. 

Aphids.  Every  one  who  has  tried  to  keep  plants  indoors 
must  have  noticed  the  small  green,  oval  insects  known  as 
plant-lice,  or  aphids.  There  are  many  species  infesting  dif- 
ferent plants,  upon  the  juices  of  which  they  feed.  Some 
attack  the  roots,  but  the  greater  number  are  found  upon  the 
foliage.  They  are  generally  not  more  than  three  millimeters 


34  GENERAL  ZOOLOGY 

(about  an  eighth  of  an  inch)  in  length,  with  a  somewhat  pear- 
shaped  body,  and  with  or  without  wings.  In  most  species 
there  is  found  projecting  from  the  back  of  the  sixth  abdom- 
inal somite  a  pair  of  slender  tubes,  which  secrete  a  sticky, 
waxen  substance,  which  is  probably  protective  in  its  nature. 
Aphids  are  sought  for  by  ants  for  the  sake  of  a  sweet  sub- 
stance called  "honeydew,"  poured  out  from  the  alimentary 
canal.  We  shall  see  later  how  certain  species  of  ants  have 
taken  to  protecting  aphids  in  order  to  secure  a  constant 
supply  of  this  food. 

The  life-history  of  some  of  the  aphids  is  most  remarkable. 
An  aphid  colony  in  the  summer  may  consist  almost  entirely 
of  wingless  females,  which  have  the  power  of  producing  gen- 
eration after  generation  of  living  young  without  fertilization. 
This  form  of  reproduction  is  known  as  parthenogenesis.  The 
young  so  produced  are  females,  and  many  of  them  are  wing- 
less, though  winged  females  are  produced  which  start  colo- 
nies in  other  places,  sometimes  on  a  different  food-plant. 
Both  winged  and  wingless  females  are  able  to  produce  young 
parthenogenetically  within  from  ten  to  twenty  days.  This 
kind  of  reproduction  goes  on  till  the  approach  of  cold  weather 
or  the  failure  of  the  food- supply,  when  males  are  produced. 
After  pairing,  the  female  lays  eggs  which  last  through  the 
winter  and  hatch  into  females  in  the  spring,  which  start  a 
new  colony  as  already  described. 

One  of  the  greatest  enemies  of  the  grape  is  an  aphid 
known  as  Phylloxe'ra  vasta'trix,  which  has  been  the  scourge 
of  many  vineyards  in  France.  It  lives  both  on  the  roots  and 
on  the  leaves.  Other  species,  called  woolly  aphids,  have  the 
power  of  secreting  a  white  downy  substance,  which  entirely 
covers  their  bodies.  One  of  these,  which  lives  in  colonies, 
making  white  masses  on  the  alder,  is  known  as  the  alder- 
blight.  This  insect  secretes  honeydew,  and  is  visited  by 
ants. 


THE   BUGS:    HEM1PTERA 


35 


Scale-Insects.  Some  of  the  greatest  enemies  to  the  horti- 
culturist are  included  among  the  scale-insects,  which  infest 
nearly  all  kinds  of  fruit-trees  and  many  shade-trees.  In  some 
species  the  body  is  scale-like  in  form ;  in  others  (Mytilas'pis 


FIG.  19.   Scale-Insect.    (After  Howard,  Year-book,  United  States 
Department  of  Agriculture,  1894) 

a,  female,  from  beneath,  showing  eggs  protected  by  scale,  X  24;  b,  female,  from 
above,  X  24;  c,  female  scale  on  branch,  natural  size;  d,  male  scale,  X  12; 
e,  male  scales  on  twig,  natural  size 

porno1  rum,  Fig.  19),  the  female,  which  begins  life  as  an  active 
insect,  soon  settles  down,  with  the  beak  fixed  in  the  tissues  of 
some  plant,  and  develops  a  waxy  scale  as  a  secretion  from  the 
skin  of  the  back,  beneath  which  she  lies  protected  for  the 
remainder  of  her  life.  The  male  is  entirely  different  in 


36  GENERAL  ZOOLOGY 

appearance  and  development.  At  first  it  resembles  the  female, 
but  it  soon  passes  into  a. short  resting,  m  pupal  stage,  beneath 
a  protecting  scale,  from  which  it  reappears  as  a  two-winged 
insect  with  rudimentary  mouth-parts.  In  this  form  of  meta- 
morphosis the  young  differs  greatly  from  the  imago,  and  there 
is  a  resting  pupal  stage  before  the  emergence  of  the  imago. 
Following  common  usage,  we  may  speak  of  this  as  a  "  com- 
plete "  metamorphosis.  The  young  is  called  a  larva. 

There  are  more  than  eight  hundred  species  of  scale-insects 
known,  and  it  is  certain  that  many  more  remain  to  be  dis- 
covered and  described.  Man  is  indebted  to  these  insects  for 
a  variety  of  products  of  greater  or  less  value.  One  of  the 
scale-insects  (Ooc'cus  cac'ti),  found  on  the  cactus  in  Mexico,  is 
the  source  of  the  red  coloring  matter,  cochineal  ;  to  another 
(Carte 'ria  lac'ca),  of  India,  we  are  indebted  for  lac.  Several 
species  produce  waxy  substances  in  use  in  various  countries 
of  the  East.  The  white  wax  of  one  Chinese  species,  formerly 
much  prized,  is  said  to  be  replaced  now  by  the  use  of  kero- 
sene. The  manna  mentioned  in  the  Book  of  Exodus  is  prob- 
ably the  secretion  of  a  scale-insect.  It  is  a  sweet  substance 
used  to-day  by  the  Arabs  as  food. 

Definition  of  Hemiptera  (Gr.  hemi,  half;  pteron,  wing). 
The  insects  mentioned  in  this  chapter  all  agree  in  possessing 
a  sucking-beak.  They  are  the  insects  to  which  the  word 
"  bug  "  is  strictly  applicable.  The  order  is  called  Hemip'tera, 
the  word  referring  to  the  fact  that  in  some  families  the  ante- 
rior wings  are  hardened  as  a  protection  for  about  half  their 
length.  Outside  of  the  cicadas  and  scale-insects  the  Hemip- 
tera develop  without  marked  metamorphosis  (see  Fig.  17). 


CHAPTER   V 
THE  BEETLES:  COLEOPTERA 

Now  fades  the  glimmering  landscape  on  the  sight, 

And  all  the  air  a  solemn  stillness  holds  ; 
Save  where  the  beetle  wheels  his  drony  flight 

And  drowsy  tinklings  lull  the  distant  folds. 

GRAY,  Elegy  in  a  Country  Churchyard. 

Tiger-Beetles  and  Ground-Beetles.  The  tiger-beetles  (Cicin- 
de'la,  Fig.  20)  will  serve  to  introduce  another  type  of  insect. 
Tiger-beetles  are  usually  metallic,  shining,  bright-colored  spe- 
cies, about  one  and  a  half  centimeters  in  length,  with  large 
heads  and  prominent  eyes,  and  are  found  on  sandy  roads  or 
beaches,  flying  about  while  the  sun  shines.  Some  of  them  are 
bright  red  or  green;  some  are  brown  or  black,  with  white 
markings ;  while  others  are  protectively  colored,  resembling 
the  sand  on  which  they  live.  They  run  swiftly,  and  when 
disturbed  take  flight,  only  to  alight  at  a  short  distance, 
often  facing  about  so  that  they  can  better  watch  the  pursuer. 
The  mouth-parts  are  all  well-developed  and  distinct,  as  in 
the  locust.  The  mandibles  are  long,  and  toothed  on  the  inner 
edge,  admirably  fitted  for  seizing  living  prey.  The  posterior 
wings  are  concealed  by  a  pair  of  hardened  wing-covers  (ante- 
rior wings),  which  meet  in  a  median  longitudinal  line  down 
the  back.  The  wing-covers  are  not  used  in  flight,  but  serve 
to  protect  the  delicate  wings  beneath. 

The  larvse  are  misshapen,  dirty-white  grubs,  living  in  holes 
which  they  dig  in  sandy  places.  Two  hooks  on  the  dorsal 
surface  enable  them  to  climb  up  and  down  in  their  holes, 
which  are  sometimes  thirty  centimeters  or  more  deep,  and 
prevent  their  being  dragged  out  when  they  have  hold  of 

37 


38 


GENERAL  ZOOLOGY 


their  prey.  Here,  with  the  earth-colored  head  even  with  the 
surface,  they  lie  in  wait,  seizing  any  passing  insect  with 
their  strong  jaws. 

Often  there  is  found  beneath  stones  in  fields  a  small  blue 
oval  insect,  about  two  centimeters  in  length,  which,  when 
handled,  emits  a  puff  of  smoke-like  gas  with  a  strong  odor, 

and  a  quite  audible  noise,  as  of 
the  report  of  a  tiny  pop-gun. 
This  is  the  bombardier-beetle 
(Brack1  inus).    Its  secretion  be- 
longs to  the  class  of  repellent 
odors,  and  may  often  render  possible  the  escape 
of  its   possessor  before  the  enemy  has  had 
time   to  recover.     The  bombardier  is  one  of 
the  large  family  of  ground-beetles  which  are 
found  beneath  sticks  and  stones  everywhere. 
Ground-beetles  are  generally  black  in  color ; 
most  of  them  capture  living  prey.    Some  have 
taken  to  cave  life  and  have  become  blind. 
In    such    cases    hairs    possessing    the    sense 
of  touch  are  well  developed  on  the  body,  so 
FIG.  20.  Tiger-Bee-  that  the  beetles   run   as  swiftly  as   if   they 
tie  and  Larva,   possessed  eyes. 

Water-Beetles.     The    whirligig-beetles 
(Dineu'tus,  Fig.  21)  are  familiar,  oval  insects  found  in  groups 


FIG.  21.   Whirligig-Beetles.     Natural  size 


THE  BEETLES:  COLEOPTERA        39 

circling  about  on  the  surface  of  still  water.  They  can  see 
both  below  and  above  the  surface  of  the  water,  as  the  two 
eyes  are  divided  into  four,  and  the  parts  separated  so  that 
watch  can  be  kept  for  danger  from  either  direction.  The 
whirligigs  are  protected  by  a  strong-smelling  milky  secretion 
which  probably  renders  them  distasteful  to  fishes.  They  are 


nor 


FIG.  22.  Diving  Beetle.    Slightly  enlarged 

able  to  dive  to  escape  danger,  carrying  down  with  them  a 
small  supply  of  air. 

Beneath  the  surface  of  such  ponds  and  pools  as  the  whirli- 
gig-beetles frequent  are  to  be  found  different  species  of  diving 
beetles  (Dytis'cm,  Fig.  22),  which  have  adaptations  similar  to 
those  mentioned  among  the  aquatic  Hemiptera.  Thus  in  some 
the  spiracles,  which  in  land  insects  are  along  the  sides  of  the 


40 


GENERAL  ZOOLOGY 


abdomen,  are  here  placed  beneath  the  edge  of  the  wing- 
covers  on  the  back,  and  the  space  beneath  the  wing-covers 
is  used  as  an  air-reservoir,  which  is  replenished  with  pure 
air  by  rising  to  the  surface.  In  other  species  a  thin  coating 
of  air  is  carried  on  the  under  side  of  the  abdomen.  This 
supply  is  obtained  by  pushing  the  head  above  water  and 
capturing  a  bubble  of  air  with  the  antennoe,  which  are  quickly 
folded  beneath  the  head,  carrying  the  imprisoned  bubble  to 
the  under  surface  of  the  body. 

Scavenger-Beetles.  A  useful  part  in  the  economy  of  nature 
is  played  by  the  scavenger-beetles  (Necroph' orus,  Fig.  23), 
large  black,  red-spotted  insects,  \vhich  dig  beneath  the  car- 
casses of  small  animals,  thus  burying  them  beneath  the 

surface.  The  female 
then  lays  her  eggs  in 
the  decaying  material, 
upon  which  the  larva) 
1  feed  until  ready  to 
transform.  This  exer- 
tion removes  the  car- 
cass from  the  field  of 
operations  of  other 
creatures  which  might 
feed  upon  it,  if  it  were 
left  exposed,  and  thus 

FIG.  23.   Scavenger-Beetle.     Slightly  enlarged     destroy   the    eggs,    or 

larvae.    As  these 

beetles  are  protected  by  a  fetid  odor,  their  striking  markings 
are  usually  spoken  of  as  an  example  of  warning  coloration, 
a  term  applied  to  those  appearances  in  animals  which  are 
thought  to  be  useful  in  notifying  enemies  of  the  presence  of 
something  disagreeable  or  dangerous. 

Lady-Beetles.  The  common  and  well-known  insects  vari- 
ously called  lady-beetles,  lady-bugs,  or  lady-birds  (CoccineVla, 


Tl 


THE  BEETLES:  COLEOPTERA        41 

Fig.  24),  are  hemispherical  in  shape  and  generally  reddish  or 
yellowish  in  color,  with  black  spots.  Both  the  imagoes  and 
larvae  of  most  species  feed  upon  plant- 
lice  and  other  insects  injurious  to  vege- 
tation ;  hence  they  are  to  be  reckoned 
among  the  insects  useful  to  the  farmer. 
A  few  years  ago,  when  the  orange- 
growing  industry  of  California  was 
threatened  with  great  loss,  if  not  total 
extinction,  from  the  attacks  of  a  scale- 
insect,  an  Australian  lady-beetle  (Veda'- 
lia)  was  introduced  to  feed  upon  it. 
The  success  of  the  experiment  was  so 
great  that  large  sums  have  been  saved 
to  the  orange-growers.  Another  scale-  FIG.  24.  Lady-Beetle. 
insect,  the  San  Jose  scale  (Aspidio'tus 

pernicio'sus),  so  called  because  it  first  appeared  many  years 
ago  in  that  city,  has  since  spread  widely  over  the  country, 
causing  great  damage  to  the  orchard  interests.  Investiga- 
tions set  on  foot  by  the  Division  of  Entomology  of  the  United 
States  Department  of  Agriculture  located  the  original  home 
of  the  insect  in  China,  and  the  discovery  was  made  there 
of  a  lady-beetle  (Chiloc'orus  sim'ilis)  which  preys  upon  it. 
This  lady-beetle  has  now  been  introduced  and  distributed  to 
infested  regions,  with  every  prospect  of  success. 

The  lady-beetles  are  protected  by  a  yellow,  odorous  fluid 
formed  in  the  blood.  '  When  the  insect  is  seized  the  fluid 
oozes  out  from  the  ends  of  the  femora.  The  bright  colors 
of  these  insects  are  usually  cited  as  an  example  of  warn- 
ing coloration. 

Click-beetles.  The  click-beetles  are  a  well-known  group, 
generally  brown  in  color  and  of  elongate  form.  The  species 
are  able  to  leap  into  the  air  when  placed  on  their  backs. 
The  mechanism  which  makes  this  possible  consists  of  a  spine 


42 


GENERAL  ZOOLOGY 


projecting  backward  on  the  ventral  surface  of  the  prothorax, 
and  a  corresponding  cavity  on  the  ventral  surface  of  the 
mesothorax.  When  the  beetle  falls  upon  its  back,  as  often 
happens  from  its  habit  of  dropping  to  the  ground  as  though 
dead,  the  legs  are  so  short  that  they  are  unable  to  help 
much  in  regaining  its  position  ;  then  the  spine  on  the  pro- 
thorax  is  driven  into  the  cavity  of  the  mesothorax  with 
force  sufficient  to  cause  the  base  of  the  wing-covers  to  strike 
against  the  surface  and  throw  the  beetle  into  the  air.  If  it 
lands  wrong  side  up,  the  act  is  repeated  until  success  crowns 
its  efforts.  The  larvae  are  called  wireworms,  and  live  in 
decaying  wood  or  attack  the  roots  of  vegetables. 

Our  largest  species  is  called  the  eyed  click-beetle  (A'laus 
ocula'tus,  Fig.  25),  on  account  of  the  oval,  eye-like  spots  on 

the  back  of  the  prothorax.  These 
spots  have  been  thought  to  be  of 
the  nature  of  terrifying  organs. 
Professor  Needham  of  Lake  Forest 
University  says:  "  If  there  be  one 
thing  more  than  another  of  which 
animals  are  suspicious,  it  is  a 
strange-looking  eye.  Nature  has 
taken  advantage  of  this  fact  in 
protecting  some  of  the  most 
innocent  little  creatures  by  devel- 
oping upon  them  spots  that  look 
like  sinister  eyes."  Several  South 
American  and  West  Indian  species 
of  click-beetles  have  the  power 
of  emitting  light  from  spots  on 
the  side  of  the  prothorax  and 
abdomen,  and  are  used  by  the 
natives  as  ornaments,  being  sewed  in  lace  and  worn  on  the 
head.  The  light  is  the  most  brilliant  and  continuous  of  any 


FIG.  25.    Eyed  Click-Beetle. 
Slightly  enlarged 


THE   BEETLES:    COLEOPTERA 


43 


luminous  insect,  though  it  is  not  given  off  when  the  insect  is 
at  rest  or  feeding. 

Fireflies.  The  power  of  giving  off  light  is  possessed  by 
the  majority  of  the  members  of  an  allied  group,  the  fireflies 
(Photu'ris,  Fig.  26),  —  soft-bodied  insects  about  two  or  three 
centimeters  in  length,  dull-colored,  and  with  the  prothorax 
usually  margined  with  red  or  yellow.  The  wing-covers  are 
much  softer  than  in  other 
beetles.  Fireflies  are,  for 
the  most  part,  nocturnal 
in  their  habits,  clinging 
to  the  under  side  of  leaves 
during  the  day.  They  are 
protected  from  the  insect- 
eating  birds  by  a  strong 
odor  which  renders  them 
distasteful.  The  lumi- 
nous spots  are  on  various 
abdominal  somites,  gen- 
erally the  last.  Fireflies 
appear  in  greatest  num- 
bers in  the  latitude  of 
the  Middle  Atlantic  states 
for  a  week  or  more  in  the 
month  of  June.  Many 
attempts  have  been  made 
to  account  for  the  light 
produced  by  the  fireflies. 
The  light-giving  organ 
seems  to  consist  of  fat- 
cells  inclosed  in  a  network  of  fine  tracheae.  These  cells 
apparently  have  the  power,  under  nervous  control,  of  secret- 
ing a  substance,  possibly  phosphureted  hydrogen,  which  is 
luminous  when  acted  upon  by  the  oxygen  furnished  by  the 


FIG.  26.   Firefly.    Slightly  enlarged 


44  GENERAL  ZOOLOGY 

tracheae.  The  process  is,  therefore,  a  form  of  oxidation.  It 
is  interesting  to  note  that  the  efficiency  of  this  apparatus  as 
a  light-producing  organ  has  been  estimated  at  100  per  cent. 
In  such  artificial  illumination  as  a  gas-jet,  for  example,  only 
about  two  per  cent  of  the  radiant  energy  consists  of  light-rays. 
The  function  of  the  light  of  the  fireflies  is  not  understood. 

Scarabs.  Certain  beetles  of  a  quite  different  group  have 
long  attracted  the  attention  of  observers  by  their  curious 
habit  of  forming  and  rolling  about  a  pellet  of  manure  for  food 
for  themselves  or  their  larvae.  We  have  several  species  of 
these  beetles  in  the  LTnited  States,  but  the  best  known  of  the 


FIG.  27.  Sacred  Beetle  and  Scarab  in  Stone,     x  2 

group  is  the  sacred  beetle  of  the  Egyptians  (Ateu'chus  sa'cer, 
Fig.  27),  the  Scarabceus  of  the  ancients,  figures  of  which  are 
found  carved  in  stone  on  the  monuments  of  ancient  Egypt. 
These  beetles  played  an  important  part  in  the  symbolism  of 
the  Egyptians,  to  whom  they  typified  the  world  and  the  sun, 
-  the  former  on  account  of  their  round  pellets,  the  latter 
on  account  of  the  projections  on  the  head,  which  were  likened 
to  the  rays  of  the  sun. 

To  the  same  group  belong  our  common  May -beetles  or  June- 
beetles  (Lachnoster'na,  Fig.  28).  These  beetles  live  in  the 
ground  in  the  larval  stage,  feeding  on  the  roots  of  plants. 


THE  BEETLES:    COLEOPTERA 


45 


The  larvae  are  the  well-known  white  grubs  often  turned  up 
by  the  plow  in  the  spring.    The  pupal  stage  is  also  passed 


FIG.  28.   Metamorphosis  of  June-Beetle.    Natural  size 

in  the  ground.    The  imagoes  feed  on  the  leaves  of  trees,  often 
completely  defoliating  them. 

Definition  of  Coleoptera  (Gr.  koleos,  sheath ;  pteron,  wing). 
The  insects  which  we  have  considered  in  this  chapter  agree  in 
possessing  biting  mouth-parts  and  hardened  sheaths  to  cover 
the  posterior  wings.  They  are  termed  beetles,  or  Ooleop'tera. 
The  Coleoptera  undergo  a  "  complete  "  metamorphosis  ;  their 
larvae  are  called  grubs. 


CHAPTER    VI 
THE  BUTTERFLIES  AND  MOTHS:    LEPIDOPTERA 

And  what 's  a  butterfly  ?    At  best 
He 's  but  a  caterpillar  drest.  —  JOHN  GAY. 

The  Monarch  Butterfly.  One  of  the  commonest  and  best 
known  of  our  butterflies  is  the  monarch,  or  milkweed  butter- 
fly (Ano'sia  plexip'pus,  Fig.  30).  It  is  a  tawny-colored  species 
expanding  about  ten  centimeters  (four  inches).  The  wings 
have  black  veins,  and  the  margins  are  black  with  white  spots. 
The  colors  are  due  to  the  presence  of  tiny  scales,  which  cover 
the  surface  regularly  and  overlap  like  the  shingles  on  a  roof. 
Besides  serving  for  the  display  of  the  colors,  the  scales  also 
strengthen  the  wings.  The  scales  are  in  origin  modified  hairs, 
like  those  which  cover  the  rest  of  the  body.  The  mouth-parts 
are  formed  for  sucking  the  nectar  of  flowers,  and  consist 
mainly  of  a  large  tubular  tongue,  or  proboscis,  which  is  coiled 
up  beneath  the  head.  The  proboscis  is  formed  from  the  length- 
ening and  union  of  the  first  maxillae.  The  mandibles  are  so 
small  as  to  be  hardly  visible.  The  anterior  legs  are  so  much 
reduced  in  size  that  they  cannot  be  used  for  walking,  and  the 
butterfly  is  therefore  practically  four-legged. 

The  monarch  passes  the  winter  in  the  South,  like  our 
migratory  birds,  and  with  approaching  warm  weather  the  dif- 
ferent individuals  slowly  work  their  way  northward,  the 
females  laying  eggs  in  different  places  in  the  course  of  the 
journey.  The  eggs  are  pale  green  and  are  deposited  singly 
on  the  leaves  of  the  different  species  of  milkweed.  In  about 
four  weeks  the  eggs  hatch  into  caterpillars,  which  immediately 
proceed  to  devour  the  egg-shells.  For  the  rest  of  their  larval 

46 


THE   BUTTERFLIES   AND  MOTHS 


47 


existence  the  caterpillars  are  voracious  feeders  on  the  leaves 
of  the  milkweed.  They  grow  for  two  or  three  weeks,  molting 
several  times  as  they  increase  in  size,  till  they  are  conspicuous 
objects,  nearly  five  centimeters  (two  inches)  long,  prominently 
banded  with  yellow  and  black  (Fig.  29).  When  through  feed- 
ing, each  larva  spins  a  pad  of  silk  on  some  convenient  support, 
and,  molting  once  more,  appears  in  a  mummy-like  pupal  con- 
dition (Fig.  29),  attached  by  hooks  at  its  extremity  to  the 
pad  of  silk  spun  by  the  larva.  In  the  pupal  stage  the  milk- 
weed butterfly  is  bright  green  with  golden  spots.  To  this, 
and  to  some  of  the  other 
naked  pupae  of  butterflies, 
the  name  chrysalis  is  some- 
times given.  The  insect  re- 
mains in  the  pupal  stage 
for  ten  or  twelve  days, 
when  the  skin  splits  and 
the  butterfly  comes  out 
with  crumpled  wings,  which 
soon  expand  and  harden. 

The  monarch  butterfly 
possesses  remarkable 
powers  of  flight.  Mr. 
Scudder,  in  his  Guide  to 
Butterflies,  mentions  that  it  has  been  seen  at  sea  five  hun- 
dred miles  from  land,  and  that  it  has  within  thirty  years 
spread  over  nearly  all  the  islands  of  the  Pacific,  and  even 
to  Australia  and  Java.  He  says :  "  Undoubtedly  carried  in 
the  first  place  by  trading  or  other  vessels  to  the  Hawaiian 
Islands,  and  thence  to  Micronesia,  it  has  unquestionably/oww 
from  island  to  island  many  hundreds  of  miles  apart.  It  has 
also  appeared  at  various  times  in  different  places  on  the 
seacoast  of  Europe ;  here  also  probably  transported  acciden- 
tally by  vessels." 


29.  .Larva  and   Pupa  of  Monarch 
Butterfly.    Natural  size 

(From  Hunter's  Studies  in  Insect  Life) 


48  GENERAL  ZOOLOGY 

It  is  asserted  that  these  butterflies,  although  so  brilliantly 
colored  and  conspicuous,  are  not  fed  upon  generally  by  birds 
and  other  animals  which  might  use  them  for  food,  owing  to 
their  possessing  a  strong  odor  which  renders  them  distasteful. 
If  this  is  the  case,  the  distinctive  coloration  may  be  an  advan- 
tage rather  than  otherwise,  making  it  easy  for  any  animal 
to  distinguish  them  from  edible  species.  The  brilliant  colors 
are  usually  cited  as  an  illustration  of  warning  coloration. 

The  Viceroy  Butterfly.  Another  butterfly  of  an  entirely 
different  genus  (see  p.  95)  and  without  any  offensive  odor, — 
the  viceroy  (Basilar'chia  archip'pm,  Fig.  30),  —  closely  resem- 
bles the  monarch.  The  viceroy  belongs  to  a  group  of  butter- 
flies whose  general  body-coloration  is  blue  and  white,  but 
instead  of  the  livery  of  its  relatives  it  wears  that  of  the  mon- 
arch. It  offers  the  best-known  illustration  in  North  America 
of  what  is  called  protective  mimicry,  a  term  applied  to  those 
cases  in  the  animal  kingdom  in  which  a  group  of  animals 
without  disagreeable  qualities  resembles,  to  a  greater  or  less 
extent,  animals  provided  with  special  means  of  defense.  Pro- 
tective mimicry  will  be  seen  to  differ  from  warning  coloration 
in  that  the  fe?n*er  is  believed  to  protect  an  animal  by  mark- 
ing it  as  a  source  of  real  danger  or  unpleasantness;  theT#fcter 
is  believed  to  protect  by  suggesting  characters  which  have 
no  existence  in  fact.  This  explanation  of  the  color  of  the 
viceroy  has  lately  been  called  in  question,  and  observations 
are  wanting  to  show  that  the  birds  of  the  eastern  United 
States  feed  generally  upon  butterflies.  Many  cases  of  pro- 
tective mimicry  are  known  among  the  butterflies  of  Africa 
and  South  America.  By  the  use  of  the  term  it  is  not  meant, 
of  course,  that  there  is  anything  conscious  in  the  mimicry. 

The  White  Mountain  Butterfly.  Another  butterfly  of  the 
same  group  is  the  White  Mountain  butterfly  (CEne'is  semid'ea), 
interesting  on  account  of  its  peculiar  distribution.  It  is  found 
only  on  the  highest  peaks  of  the  White  Mountains  in  New 


VIG.  30.    Monarch.  Viceroy,  and  Type  Baailarrhin.    Natural  size 

Upper  figure,  the  monarch  butterfly  (Anosia plexippus) ;  middle  figure,  the  viceroy 
butterfly  (BasUarchia  archippus) ;  lower  figure,  another  species  of  the  genus 
Bcurilarchia,  to  show  the  usual  coloration  of  the  genus 


THE   BUTTERFLIES  AND  MOTHS  49 

Hampshire  and  the  Rocky  Mountains  in  Colorado.  As  will 
be  seen  later,  the  geological  period  immediately  preceding  the 
present  was  an  age  of  ice,  in  which  the  North  American  conti- 
nent was  covered  by  ice  as  far  south  as  an  irregular  line  drawn 
through  New  York,  Pennsylvania,  Missouri,  South  Dakota, 
and  Oregon,  and  arctic  conditions  existed  over  the  rest  of 
the  continent.  At  this  time  these  butterflies  were  probably 
distributed  over  the  country.  As  the  ice  slowly  melted  and 
the  climate  became  warmer,  they  found  only  on  the  summits 
of  these  widely  separated  mountain  ranges  the  conditions  to 
which  they  had  been  accustomed,  all  those  occupying  the 
region  between  being  driven  to  the  northward  or  destroyed 
by  the  heat. 

Swallow-Tail  Butterflies.  The  magnificent  insects  called 
swallow-tail  butterflies,  widely  distributed  over  the  world, 
have  received  their  common  name  on  account  of  the  prolon- 
gation of  the  posterior  wings.  They  are  especially  interest- 
ing to  the  naturalist,  not  only  for  the  variety  and  beauty  of 
their  colors  and  the  elegance  of  their  form,  but  also  because 
they  often  exhibit,  within  the  limits  of  a  single  species,  great 
variation  in  color,  size,  and  even  in  the  shape  of  the  wings. 
The  variation  in  form,  size,  and  color  between  individuals  of 
the  same  species  is  spoken  of  as  dimorphism  (Gr.  di,  two ; 
morphe,  form),  if  the  variations  show  two  well-marked  types ; 
and  as  polymorphism  (Gr.  poly,  many),  if  there  are  several 
different  variations.  In  many  species  the  males  differ  greatly 
from  the  females  ;  this  is  called  sexual  dimorphism.  Many  ex- 
amples are  known  of  broods  of  the  same  butterfly  appearing 
at  two  different  seasons.  These  broods  often  differ  widely  in 
size  and  color  markings.  This  is  known  as  seasonal  dimor- 
phism. In  some  cases  seasonal  dimorphism  and  polymorphism 
seem  to  result  from  conditions  of  temperature.  A  swallow- 
tail butterfly  (Papil'io  a'jax),  which  is  widely  distributed  in  the 
eastern  United  States,  has,  in  the  latitude  of  West  Virginia, 


50 


GENERAL  ZOOLOGY 


three  different  forms,  called  the  early  spring,  the  late  spring, 
and  the  summer  form.  Both  of  the  spring  forms  appear  from 
pupae  which  have  lived  through  the  winter.  From  the  eggs 
which  the  spring  forms  lay  the  summer  form  develops  several 
successive  broods  the  same  year. 

Skippers.    The  skippers  (Epargy'rem  tit'yrus,  Fig.  31)  are, 
like  the  butterflies,  diurnal  insects,  and  are  found  in  fields 


and  along 
woods  ides, 
where  they 
dart  about 

in  a  most  erratic  manner.  They  are 
closely  allied  to  the  butterflies,  but 
differ  from  them  in  several  details 
of  structure  and  habits.  The  butter- 
flies (see  Fig.  30)  have  club-shaped 
antennae,  while  in  the  skippers  the 
antennae,  though  enlarged  at  the 
end,  are  generally  recurved,  forming 
a  hook.  The  skippers  have  stouter 
bodies  than  the  butterflies,  and  most 
of  them  hold  the  wings  upright  after 
the  fashion  of  the  butterflies ;  but 
some  hold  only  the  anterior  wings  in  this  position.  The  larvse 
of  those  species  found  in  the  United  States  can  easily  be  dis- 
tinguished from  other  caterpillars  by  the  very  large  head  and 
strongly  constricted  neck  (Fig.  31).  They  usually  live  in  a 
folded  leaf,  or  in  a  nest  of  leaves,  and  pass  the  pupal  stage  in  a 
thin  cocoon  of  silk  spun  by  the  caterpillars  before  changing.  In 
this  latter  respect,  too,  the  skippers  differ  from  the  butterflies, 
since  the  latter  (as  shown  in  Fig.  29)  have  a  naked  pupal  stage. 


FIG.  31.   Metamorphosis  of 
Skipper.    Natural  size 


THE  BUTTERFLIES  AND  MOTHS  51 

Silkworm  Moths.  Allied  to  both  butterflies  and  skippers 
is  the  great  group  of  moths,  —  stout-bodied  insects,  the 
antennse  of  which  are  usually  feather-like  or  thread-like 
(Figs.  32,  33,  34).  Moths  have  the  habit  of  holding  the 
wings  horizontal  when  at  rest.  They  are  nocturnal  or  diur- 
nal in  their  habits,  though  by  far  the  larger  number  fly  by 
night.  Most  of  them  spin  some  kind  of  a  cocoon  in  which 
they  pass  the  pupal  stage. 

We  shall  first  consider  the  silkworm  moths.  Of  these  the 
best  known,  as  it  is  economically  the  most  important,  is 
the  Chinese  silkworm  moth  (Bom1  by x  mo'ri).  Cultivated  in 
China  from  very  early  times,  the  Chinese  jealously  guarded 
the  secrets  of  the  manufacture  of  silk  until,  as  the  story  goes, 
in  the  middle  of  the  sixth  century  two  monks  brought  the 
eggs  to  Constantinople  by  stealth,  concealed  in  a  hollow  bam- 
boo cane.  The  cultivation  of  the  silkworm  then  spread  rapidly 
to  those  parts  of  Europe  suited  to  its  culture.  It  was  intro- 
duced into  England  in  the  fifteenth  century,  but  the  manu- 
facture of  silk  was  given  no  impetus  till  the  arrival  in  1585 
of  a  body  of  Flemish  weavers,  who  had  fled  from  the  Low 
Countries  on  account  of  the  struggle  with  Spain.  One  hun- 
dred years  later  the  revocation  of  the  Edict  of  Nantes  drove 
a  large  body  of  skilled  workmen  from  France  to  England, 
Germany,  and  Switzerland,  and  the  silk-manufacturing  indus- 
try developed  still  more  in  these  three  countries.  From  1609 
to  the  present  day  various  efforts  have  been  made  to  intro- 
duce silk  culture  into  the  United  States,  the  plan  of  bounties 
and  rewards  to  stimulate  its  growth  having  been  tried  by  the 
rulers  in  colonial  days,  and  by  several  states  since  the  war 
of  1861-65.  These  artificial  means  have  so  far  not  met  with 
great  success.  In  China  the  caterpillar  thrives  best  on  the 
leaves  of  the  white  mulberry,  but  it  has  been  found  to  do 
well  on  the  Osage  orange,  a  tree  widely  distributed  in  the 
south  and  west  of  the  United  States. 


52  GENERAL  ZOOLOGY 

The  silk-glands  extend  through  the  body  of  the  caterpil- 
lar and  open  into  the  mouth.  Toward  the  time  of  pupation 
they  increase  in  size  and  produce  about  four  thousand  yards 
of  material,  which,  on  being  exposed  to  the  air,  hardens  and 
becomes  the  silk  of  commerce.  As  there  are  two  sets  of  these 
glands,  each  silk  filament  is  really  double.  Within  this  cocoon 
of  silk  the  larva  casts  its  caterpillar  skin  and  becomes  a  pupa. 
In  silk-culture  the  cocoons  are  placed  in  an  oven  to  kill  the 
pupae,  and  the  silk  is  softened  by  being  placed  in  warm  water. 
Then,  by  means  of  a  twig  moved  about  among  the  cocoons, 
loose  ends  of  several  of  them  are  caught,  united  into  one 
thread,  and  wound  on  a  reel,  which  is  placed  at  a  distance 
from  the  hot  water  so  that  the  silk  may  dry.  This  is  the 
raw  silk  of  commerce. 

We  have  several  large  moths  in  the  United  States,  expand- 
ing from  ten  to  fifteen  centimeters  (four  to  six  inches),  whose 
larvae  spin  silken  cocoons,  some  of  which  have  been  utilized 
to  a  limited  extent  by  man.  They  are  magnificent  insects, 
with  broad  wings  beautifully  colored,  and  with  large  feather- 
like  antennse.  The  larvae  feed  on  the  leaves  of  forest  and 
fruit  trees,  and  are  more  or  less  armed  with  a  variety  of 
colored  spines  and  tubercles.  The  caterpillars,  like  other 
larvse  which  feed  upon  plant  food,  are  remarkable  for  the 
amount  of  food  which  they  consume  and  the  great  increase 
in  size  in  early  life.  The  caterpillar  of  the  American  silk- 
worm moth  (Te'lea  polyphe'mus),  which  weighs  on  hatching 
one  twentieth  of  a  grain,  increases  to  ten  times  its  weight 
within  ten  days,  and  to  over  four  thousand  times  its  weight 
in  fifty  days.  By  this  time  it  has  consumed  over  one  hundred 
oak  leaves,  weighing  almost  three  quarters  of  a  pound,  and 
drunk  nearly  one  half  an  ounce  of  water.  The  larvae  of  these 
moths  spin  conspicuous  brown  cocoons,  which  can  easily  be 
collected  in  the  winter  from  the  branches  and  leaves  of  trees 
to  which  they  are  attached.  In  the  spring  the  imagoes  escape 


THE   BUTTERFLIES   AND   MOTHS 


53 


from  one  end  of  the  cocoons  by  cutting  the  silk  with  a  pair  of 
stout  spines,  one  on  each  side  of  the  thorax,  at  the  base  of 
the  anterior  wings. 

Underwings.  A  very  striking  group  of  moths  is  the  under- 
wings  (Catoc'ala,  Fig.  32),  which  have  the  anterior  wings  in 
sober  tints  of  brown 
or  gray,  but  the  pos- 
terior wings  black 
with  broad  mark- 
ings of  red  or  yel- 
low. When  at  rest, 
as  shown  in  the 
figure,  the  posterior 
wings  are  covered 
and  the  moth  tends 
to  be  protectively 
colored ;  but  when 
in  flight  the  broad, 
contrasting  colors 
are  conspicuous.  It 
is  usual  to  account 
for  the  coloration  of 
the  anterior  wings 
by  the  principle  of 

protective  resem-  FIG.  32.  Underwing  at  Rest.    Reduced 

blance.  Some  nat- 
uralists have  thought  that  the  bright  colors  of  the  posterior 
wings  demand  no  other  explanation  than  that  they  have 
resulted  from  a  natural  tendency  to  bright  colors ;  while 
others  have  suggested  that  they  serve  to  call  attention  to  a 
non-vital  part. 

Hawk-Moths.  The  hawk-moths  or  sphinx-moths  (Fig.  33) 
are  easily  recognized  by  the  stout  conical  body,  long  coiled 
proboscis,  narrow  pointed  wings,  and  the  slender  antennae. 


•> 

f 


54 


GENERAL  ZOOLOGY 


They  are  dressed,  for  the  most  part, 

in  quiet  olive  and  brown  tints,  and  fly         J 

by  day.    Their  larvae  are  large,  naked        //. 

4 


caterpillars,  often  with  a 
curved  horn  near  the  pos- 
terior extremity.  They 
have  the  habit  of  resting 
with  the  head  and  front 
of  the  body  raised  in 
the  air.  In  this  attitude 
they  have  been  fancied 
to  resemble  the  Egyptian 
sphinx.  It  has  been 
thought  by  some  zoolo- 
gists that  this  position  is 
assumed  as  a  terrifying 
attitude.  The  tobacco- 
worm  is  the  larva  of  the 


FIG.  33.   Metamorphosis  of  Sphinx-Moth. 
Reduced 


THE  BUTTERFLIES   AND   MOTHS 


55 


well-known  species,  Phlegethon'tim  sex'ta  (Fig.  33),  found  on 
tomato,  potato,  and  tobacco  plants.     The  larva,  though  often 


credited  with  poisoning  people  by  sting- 
ing them  with  the  long  curved  caudal  horn, 
is  in  reality  entirely  harmless.  The  pupa 
is  remarkable  for  the  long  coiled  proboscis- 
case. 

Tussock-Moths.  The  tussock-moths, 
though  few  in  number  of  species  and  incon- 
spicuous in  the  adult  stage,  are  compara- 
tively well  known  from  their  conspicuous 
larvse,  which  are  clothed  with  white  or 
brightly  colored  tufts  of  hair.  The  white- 
marked  tussock-moth  (NotoV ophus  leuco- 
stiy'ma,  Fig.  34)  is  the  commonest  species 
in  the  eastern  United  States.  The  head 
and  some  body-spots  are  bright  red.  A 
black  stripe  runs  down  the  middle  of  the 
back  and  yellow  stripes  occur  on  either 

FIG.  34.    Metamor-    g^e.     Long   brushes    of    black   hairs    are 
phosis  of  Tussock-    .  ,  -11-1 

Moth.  Natural  size    borne    anteriorly    and    posteriorly,    while 

four  dense  clusters  of  white  hairs  stand 
up  prominently  from  just  behind  the  head.  The  females  are 
wingless  and  look  more  like  white  grubs  than  moths.  When 


56 


GENERAL  ZOOLOGY 


they  emerge  from  the  cocoons  the  eggs  are  laid  near  by,  often 
on  the  cocoons.  Fig.  34  shows  the  female  in  the  act  of 
laying  eggs  in  such  a  situation. 

Observations  on  the  food  of  birds  of  the  eastern  United 
States  seem  to  show  that  the  spines,  tubercles,  and  hairs, 
with  which  many  caterpillars  are  covered  (compare  Fig.  35, 
the  larva  of  the  regal  moth,  Cithero'nia  rega'lis),  form  very 
efficient  means  of  protection,  —  at  least  from  birds,  —  since, 

with  the  exception   of   the 

[•••HI  '  - , 

cuckoo,  no  bird  is  known  to 
make  a  practice  of  feeding 
on  hairy  caterpillars.  Pro- 
fessor Poulton  of  Oxford, 
England,  experimented  with 
a  species  of  tussock-moth 
from  England  to  determine 
the  part  the  tufts  of  hair 
play  in  the  life-economy  of 
the  caterpillar.  He  says : 
"  A  caterpillar  of  the  com- 
mon vaporer  moth  (Oryg'ia 
anti'qua)  was  introduced  in- 
to a  lizard's  cage,  and  when 
attacked  instantly  assumed 
the  defensive  attitude,  with 
the  head  tucked  in  and  the 
tussocks  separated  and  ren- 
dered as  prominent  as  pos- 
sible. An  unwary  lizard 
seized  the  apparently  convenient  projection ;  most  of  the 
tussock  came  out  in  its  mouth,  and  the  caterpillar  was  not 
troubled  further.  The  lizard  spent  a  long  and  evidently 
most  uncomfortable  time  in  trying  to  get  rid  of  its  mouthful 
of  hairs." 


FIG.  35.   Larva  of  Regal  Moth. 
Reduced 


THE  BUTTERFLIES  AND  MOTHS  57 

Measuring- Worms.  The  measuring- worms  (Fig.  36)  are  the 
larva;  of  a  group  of  medium-sized  moths,  which  afford  many 
illustrations  of  protective  re- 
semblance. When  some  of 
these  larvae  are  at  rest,  stand- 
ing out  stiff  from  a  twig,  it  is 
difficult  to  believe  them  to  be 
caterpillars.  Most  of  them 
have  three  pairs  of  legs  less 
than  other  caterpillars,  so  that 
a  looping  gait  is  the  result, 
whence  the  name,  "  measuring- 
worms."  They  have  the  habit, 
when  disturbed,  of  dropping 
to  the  ground  on  a  silken 
thread,  which  they  spin  as  they 
fall. 

Definition  of  Lepidoptera 
(Gr.  lepis  (lepidos),  scale; 
pteron,  wing).  The  butterflies, 
skippers,  and  moths,  collec- 
tively, are  spoken  of  as  Lepi- 
dop'tera.  The  Lepidoptera 
have  four  large  wings  covered 
with  scales,  sucking  mouth- 
parts,  and  undergo  a  "  com- 
plete" metamorphosis.  The 
larvae,  called  caterpillars,  with 
few  exceptions,  feed  upon  the 
leaves  of  plants.  They  pass  a 
greater  length  of  time  in  the 
pupal  stage  than  the  other 
insects  we  have  thus  far  con-  FR;  36  Measuring_Worms.  Natural 
sidered.  size 


CHAPTER  VII 


THE  FLIES:  DIPTERA 

.   .   .  like  small  gnats  and  flies  as  thick  as  mist 
On  evening  marshes.  — SIIKLLEY. 

House-Flies  and  Flesh-Flies.  The  common  house-fly  (Mus'ca 
domes' tica,  Fig.  37)  is  a  cosmopolitan  insect.  The  eyes  are 
very  large,  occupying  the  whole  side  of  the  head;  the  an- 
tennae are  short  and  composed  of  only  three  joints,  the  third 

bearing  a  bristle. 
The  mouth-parts 
are  formed  for 
sucking  and  lap- 
ping. They  consist 
of  a  short  tongue- 
like  proboscis,  with 
large  oval  flaps,  or 
lobes,  on  each  side. 
These  flaps  are 
extensile,  and  are 
roughened  like  a 
file  on  the  inner 
surface,  thus  per- 
mitting of  their 
use  as  a  scraper, 
by  means  of  which  the  insect  can  lap  up  sweets  or  other  food. 
The  proboscis  is  made  up  of  the  united  maxillae.  The  thorax 
is  globular  and  bears  but  one  pair  of  wings,  though  the  rudi- 
ments of  others,  called  "  balancers,"  can  be  seen  in  the  form 
of  two  little  round  objects,  borne  on  slender  stalks.  These 

58 


FIG.  37.  Metamorphosis  of  House-Fly.    Enlarged 


THE  FLIES:    DIPTERA  59 

balancers  also  act  as  organs  of  hearing.  Two  broad  scales 
are  found  on  the  sides  of  the  thorax,  just  behind  the  wings. 
The  legs  are  fitted  for  running,  and  the  pulvilli  are  large 
and  bear  tubular  hairs,  which  secrete  a  sticky  fluid  by  means 
of  which  the  fly  can  walk  on  smooth  surfaces,  even  when 
upside  down. 

The  eggs,  over  one  hundred  in  number,  are  laid  usually 
in  horse-manure,  and  hatch  within  a  day  into  smooth  white, 
almost  transparent,  conical,  footless  larvae,  called  maggots. 
They  have  rudimentary  mouth-parts,  consisting  only  of  a 
few  small  hooks.  The  larvse  feed  for  about  a  week,  growing 
rapidly  and  molting  twice  within  that  time,  and  then  pass 
into  an  inactive  pupal  stage  within  the  larval  skin.  In  a  week 
more  the  perfect  insect  appears  by  making  a  circular  hole 
in  one  end  of  the  pupal  case  by  means  of  a  large  bladder- 
like  bulb,  which  swells  out  on  the  forehead  and  is  later  with- 
drawn into  the  head.  The  life-history  is  thus  completed 
within  about  two  weeks,  and  as  the  imagoes  soon  lay  eggs, 
there  may  be  several  generations  in  the  course  of  the  summer. 
On  the  approach  of  cold  weather  most  of  them  die,  though 
some  hibernate  in  sheltered  places. 

The  house-fly  has  always  been  considered  a  nuisance  about 
the  house  ;  but  lately  a  more  serious  charge  has  been  laid  at 
its  door,  —  that  of  transporting  on  the  pulvilli  and  proboscis 
the  germs  of  typhoid  fever..  With  the  knowledge  of  its  favorite 
breeding-place  it  should  be  possible,  by  insisting  on  cleanli- 
ness in  stables,  by  the  daily  collection  of  manure  and  its  dis- 
posal in  a  closed  place,  or  by  treatment  with  chloride  of  lime,  to 
greatly  mitigate,  if  not  entirely  destroy,  this  menace  to  health. 

Equally  well  known  are  the  blow-fly  (Calliph'ora  vomito'ria) 
and  the  bluebottle  (Lucil'ia  cae'sar),  which  deposit  their  eggs 
on  fresh  and  decaying  meat.  These  flies  hatch  within  a  day, 
and  the  larvas  greedily  devour  the  decaying  material,  not 
hesitating,  when  that  task  is  finished,  to  devour  each  other. 


60 


GENERAL  ZOOLOGY 


The  famous  tsetse  fly  of  South  Africa  (Crlossi'na  mor'sitans), 
whose  bite  is  almost  certainly  fatal  to  the  ox,  horse,  and  dog, 
belongs  to  the  same  family  as  the  species  just  mentioned.  It 
has  been  found  almost  impossible  to  build  up  certain  sections 
of  South  Africa,  owing  to  the  prevalence  of  this  insect.  An 
English  army  surgeon  has  lately  discovered  that  by  its  bite 
it  introduces  disease  germs  from  sick  animals  into  the  blood 
of  healthy  ones. 

Bot-Flies.  The  bot-flies  are  parasites  in  the  larval  stage ; 
that  is,  they  live  in  the  bodies  of  other  animals.  There  are 


B  D 

FIG.  38.  Metamorphosis  of  Horse  Bot-Fly.  (After  Osborn,  Bulletin  No.  -5,  N.S., 
United  States  Department  of  Agriculture,  Division  of  Entomology) 

A,  egg  on  hair  of  horse  (natural  size) ;  B,  egg  on  hair  of  horse  (enlarged) ; 
C,  young  larva  (enlarged) ;  D,  young  larva  (much  enlarged) ;  E,  spines ; 
F,  full-grown  larva  (twice  natural  size) ;  G,  female  (natural  size) 

nearly  one  hundred  species  known,  infesting  various  animals, 
living  either  under  the  skin,  in  the  nostrils,  or  in  the  stomach. 
The  bot-fly  of  the  horse  (G-astroph'ilus  e'qui,  Fig.  38)  attaches 
its  eggs  singly  by  means  of  a  sticky  substance  to  the  hairs  of 
the  legs,  where  the  larva  is  pretty  sure  to  be  swallowed  when 
the  animal  licks  or  bites  its  legs  to  remove  the  irritation. 


THE  FLIES:    DIPTERA  61 

The  larva  then  attaches  itself  to  the  lining  of  the  stomach 
by  means  of  hooks,  which  encircle  the  mouth,  and  for  nearly 
a  year  feeds  on  the  substance  of  the  stomach-wall.  The  pupal 
stage  is  passed  in  the  earth,  which  is  reached  through  the 
alimentary  canal.  A  few  of  these  parasites  do  110  particular 
harm,  but  a  large  number  may  cause  death. 

The  sheep  bot-fly  ( (Es'trus  o'vis)  in  a  similar  manner  attacks 
the  nostrils  of  sheep.  The  appearance  of  one  of  these  flies 
in  a  flock  of  sheep  is  sufficient  to  throw  them  into  a  state 
of  panic  ;  they  run  about  with  their  noses  between  their 
legs,  or  try  to  bury  them  in  dust,  to  escape  their  tormentors. 
The  female  bot-fly  does  not  lay  her  eggs  as  do  most  other 
insects,  but  retains  them  within  her  body  till  they  hatch, 
and  then  deposits  the  living  young,  —  that  is  to  say,  she  is 
viviparous. 

Hover-Flies.  Often  a  collector  captures  an  insect  flying 
about  flowers,  which  has  the  characteristic  manner  and  yellow 
and  black  colors  of  a  wasp,  but  which  has  only  two  wings. 
It  is  one  of  the  hover-flies,  many  of  which  afford  illustrations 
of  protective  mimicry.  Some  species  of  Eris'talis  (Fig.  45) 
mimic  the  male  honey-bee,  and  are  therefore  named  drone- 
flies  ;  others  belonging  to  Volucel'la  (Fig.  45)  mimic  bumble- 
bees. The  larvae  of  some  feed  upon  aphids,  and  are  therefore 
beneficial  to  the  farmer ;  others  inhabit  pools  of  stagnant 
water  or  decaying  wood.  Several  are  called  rat-tailed  larvae, 
from  the  presence  of  a  long  tube  projecting  from  the  pos- 
terior end  of  the  body,  which  enables  the  larva  to  get  air 
when  submerged.  The  larva  of  the  drone-fly  is  of  this  type. 
Other  species  are  found  in  ants'  nests. 

Mosquitoes.  The  mosquitoes  are  a  group  widely  distributed 
over  the  tropical  and  temperate  regions  of  both  hemispheres. 
In  nearly  all  the  species  observed  the  mouth-parts  of  the 
females  only  are  fitted  for  piercing  the  skin  of  animals. 
The  males,  if  they  feed  at  all,  probably  suck  the  fluids  of 


GENERAL  ZOOLOGY 


plants ;   in  fact,  both  sexes  in  the  past  history  of  the  race 
were  probably,  and  are  still,  to  some  extent,  plant-feeders. 

The  common  mos- 
quito of  the  Missis- 
sippi valley  and  the 
East  is  Cu' lex  pun' gens 
(Fig.  39).  The  female 
lays  her  eggs  in  irreg- 
ular masses,  contain- 
ing over  two  hundred 
eggs,  on  the  surface 
of  the  water  early  in 
the  morning.  Within 
a  day  they  hatch,  and 
the  larva?  are  the  fa- 
miliar, active  creatures 
known  as  "wrigglers." 
The  next  to  the  last 
Enlarged,  somite  bears  a  long 
s.,  United  respiratory  tube 


of  Entomology) 

A,  egg-mass;  -B,  larva;  C,  pupa 


FIG.  39.  Development  of  Mosquito. 
(After  Howard,  Bulletin  No.  25,  N 
States  Department  of  Agriculture,  Division    througb    wh;ch   the 

larva  breathes  air  when 
at  the  surface  ;  the  last 
somite  is  provided  with  four  flaps  (tracheal  gills)  which  act 
as  organs  of  respiration  when  the  larva  is  beneath  the  surface. 
In  addition  to  these  methods  of  obtaining  air,  the  skin  is 
capable  of  absorbing  oxygen,  and  a  network  of  trachea  lines 
the  posterior  part  of  the  alimentary  canal,  so  that  oxygen 
may  be  obtained  from  the  water  taken  in  at  the  anal  opening. 
The  Iarva3  feed  on  small  particles  of  decaying  matter  in  the 
water,  thus  being  useful  as  scavengers.  After  several  molts 
and  a  life  of  about  a  week,  if  the  weather  is  warm  they  then 
pass  into  the  pupal  stage,  breathing  by  means  of  two  air- 
tubes  arising  from  the  thorax.  In  about  two  days  the  pupal 


THE  FLIES:    DIPTERA  63 

skin  splits  down  the  back  and  the  imago  works  itself  out  of 
its  old  skin,  dries  its  wings,  and  flies  away.  Cold  weather 
retards  these  changes  considerably. 

Great  interest  attaches  to  the  mosquitoes  by  reason  of  the 
recent  indictment  that  some  species  transmit  malaria  and 
yellow  fever.  Malaria  is  carried  by  mosquitoes  belonging  to 
the  genus  Anoph'eles, 
the  females  of  which 
may  be  distinguished 
from  the  females  of 
Culex  by  the  greater 
length  of  the  palpi  FlG-  40-  Resting  Positions  of  Anopheles  and 

The  males  of  both  Culex'  Slightly  enlarge(L  <After  Grassi) 
genera  can  be  distinguished  from  the  females  by  their  more 
feathery  antennae.  Anopheles  shows  a  tendency,  especially 
on  horizontal  surfaces,  to  alight  with  the  hind  end  of  the 
body  raised  at  a  considerable  angle  to  the  surface ;  Culex 
holds  the  body  parallel  to  the  surface.  In  Anopheles  the 
body  and  beak  are  in  the  same  plane  no  matter  what  the 
position  is  ;  Culex  is  humpbacked,  with  the  beak  pointing 
downward.  These  various  distinctions  are  well  shown  in 
Fig.  40.  The  disease  known  as  malaria  is  caused  by  the  pres- 
ence in  the  blood  of  a  parasitic  organism,  one  of  the  lowest 
forms  of  animal  life,  known  as  Plasmo'dium  mala' rice.  Its  rapid 
development  at  certain  stages  produces  the  well-known  fever 
connected  with  the  disease.  The  life-history  of  the  organism 
is  described  in  Chapter  XXI.  The  most  extensive  experi- 
ments concerning  the  connection  between  the  Anopheles 
mosquito  and  malaria  have  been  carried  on  by  the  British 
Colonial  Office  and  the  British  School  of  Tropical  Medicine. 
Two  physicians,  under  the  auspices  of  these  institutions,  estab- 
lished themselves  in  the  fever-infected  Roman  Campagna. 
They  took  no  special  precaution  against  the  disease,  drinking 
the  water  of  the  district  and  in  other  ways  conforming  to  the 


64  GENERAL  ZOOLOGY 

customs  of  the  people,  save  only  that  they  did  not  allow  them- 
selves to  be  bitten  by  the  Anopheles  mosquito,  which  swarms 
in  that  region  at  the  close  of  day.  They  slept  during  the 
night  in  a  mosquito-proof  house,  and  did  not  contract  malaria. 
Persons,  on  the  other  hand,  with  no  traces  of  malaria,  have 
allowed  themselves  to  be  bitten,  and  thus  contracted  the 
disease.  It  seems,  from  these  and  other  experiments,  that  the 
malarial  parasite  is  injected  into  the  blood  with  the  saliva  of 
the  insect,  and  it  further  appears  that,  in  order  to  complete 
the  life-history  of  the  parasite,  it  must  enter  the  salivary 
gland  of  the  mosquito.  Quinine  is  a  specific,  because  it  kills 
the  organism  at  a  certain  stage  in  its  life-history.  United 
States  army  surgeons  in  Cuba  have  been  instrumental  in 
clearing  up  the  life-history  of  the  yellow-fever  germ,  which 
seems  to  be  transmitted  by  mosquitoes  of  the  genus  Stegom'yia. 

Many  localities  can  be  practically  rid  of  these  pests  by  the 
drainage  of  the  swamps  or  ponds  in  which  they  breed;  by 
the  use  of  kerosene  on  the  surface  of  such  waters ;  or  by 
the  introduction  of  fish  that  feed  on  the  larvse.  Among  the 
fishes  recommended  are  sunfish  and  sticklebacks.  It  must 
be  remembered  that  the  insect  will  breed  successfully  in  any 
transient  pool  of  water,  or  in  any  receptacle  where  water  is 
left  standing  long  enough  for  the  changes  just  described  to 
take  place.  Experiments  are  being  conducted  in  the  Middle 
West  with  a  fungous  disease  similar  to  that  which  destroys 
large  numbers  of  flies  in  the  autumn. 

Definition  of  Diptera  (Gr.  dipteros,  two-winged).  The  in- 
sects collectively  called  flies  agree  in  the  possession  of  two 
wings,  the  place  of  the  posterior  pair  being  taken  by  the  bal- 
ancers, which  may  therefore  be  considered  reduced  wings. 
The  flies  belong  to  the  order  Dip'tera.  The  Diptera  have  the 
mouth-parts  fitted  for  sucking  or  piercing.  They  undergo  a 
"  complete  "  metamorphosis.  The  larvse  are  commonly  known 
as  maggots. 


CHAPTER   VIII 
THE  ANTS,  BEES,  AND  WASPS :  HYMENOPTERA 

For  so  work  the  honey-bees, 
Creatures  that  by  a  rule  in  nature  teach 
The  art  of  order  to  a  peopled  kingdom. 

SHAKESPEARE,  King  Henry  V. 

Social  Wasps.  The  common  brown  wasps  (Polis'tes,  Fig.  41) 
are  interesting  on  account  of  their  communal  life  in  nests  of 
paper  made  from  wood-pulp.  The  mouth-parts  are  fitted  both 
for  biting  hard  substances  and  also  for  lapping  the  fluids  of 
plants.  The  mandibles  are  much  the  same  as  in  such  biting 
insects  as  the  locusts ;  the  first  maxillae  are  elongate,  sharp- 
pointed,  lance-like  organs,  and  the  second  maxillse  are  modi- 
fied into  a  flexible,  tongue-like  structure  covered  with  hairs, 
to  which  sweets  adhere.  There  are  four  membranous,  trans- 
parent wings,  with  few  veins.  The  female  is  provided  with 
a  formidable  sting,  —  an  important  means  of  defense,  — 
which  is  in  origin  a  modified  ovipositor. 

Early  in  the  spring  a  female  Polistes,  which  has  wintered 
in  a  crevice,  begins  the  construction  of  a  nest  in  some  suitable 
place,  either  on  the  under  side  of  a  roof,  especially  in  deserted 
houses  or  barns,  or  on  the  ground  beneath  a  stone.  If  there 
are  fences  or  barns  in  the  region,  she  will  very  likely  obtain 
a  supply  of  wood  from  them ;  if  not,  from  stumps  and  dead 
trees.  After  being  chewed  by  her  and  moistened  by  a  secre- 
tion from  her  mouth,  this  material  is  fashioned  by  the  feet 
and  mandibles  into  circular  cells,  which  become  hexagonal 
as  their  number  is  added  to  and  the  pressure  increases.  The 
whole  is  waterproofed  by  a  glutinous  secretion,  which  is 
said  to  be  increased  in  amount  in  those  cells  which  are  most 

65 


66  GENERAL  ZOOLOGY 

exposed  to  the  weather.  As  soon  as  one  cell  is  finished  the 
female  lays  an  egg  in  it,  and  to  her  duty  of  enlarging  and 
strengthening  the  nest  she  soon  lias  to  add  the  care  of  the 
footless,  worm-like  larvae,  which  hatch  in  a  few  days.  These 
are  fed  with  both  plant  and  animal  food,  the  former  consist- 
ing of  nectar  which  has  been  swallowed  and  later  regurgitated 
(i.e.  thrown  back  after  being  swallowed) ;  the  latter,  of  cater- 
pillar meat  chopped  fine  by  the  mandibles  and  worked  into 
a  jelly-like  mass.  In  about  three  weeks'  time  the  first-born 
larvae  spin  a  silken  lining  and  covering  to  the  cell  and  pass 
into  an  inactive  pnpal  stage.  Three  weeks  later  the  first 
imagoes  appear,  after  having  cut  a  circular  opening  in  the 
end  of  the  cell. 

These  first  imagoes  differ  somewhat  from  their  mother, 
and  are  really  imperfectly  developed  females,  called  neuters, 
or  workers.  They  have  the  power,  under  certain  conditions, 
of  laying  eggs,  but  their  eggs  never  produce  true  females. 
Generally  the  workers  attend  strictly  to  the  business  of  caring 
for  the  young  and  repairing  and  enlarging  the  nest.  They 
assume  care  of  the  young  at  about  the  third  day. 

This  habit  may  be  due  primarily  to  imitation  of  the  female, 
whom  the  worker  sees  repeating  the  act  while  it  is  waiting 
for  the  hardening  of  its  tissues,  or  to  the  early  development 
of  an  instinctive  tendency  to  perform  the  act  (see  p.  85). 
Experiments  performed  by  Dr.  Enteman  of  the  University 
of  Chicago,  in  which  newly  developed  workers  were  given 
bits  of  food  at  intervals  before  they  had  had  any  association 
with  others  of  their  kind,  seem  to  show  that  it  is  an  instinct 
which  appears  very  early,  but  not  at  the  same  time  with 
all  workers.  When  it  does  appear,  owing  to  the  presence  of 
food  furnished  by  the  female,  the  steps  are,  according  to 
Dr.  Enteman,  "  first  the  crushing  and  molding,  then  a  slow 
walking  around  the  nest  with  frequent  pauses,  and,  if  larvae 
are  present,  the  pinching  off  of  the  food  bit  by  bit  until  all 


THE  ANTS,  BEES,  AND  WASPS  67 

has  been  disposed  of.  If  no  larvse  are  present,  —  if,  for 
instance,  the  young  worker  is  living  in  an  inverted  tum- 
bler and  has  never  seen  a  larva,  —  the  various  stages  of  the 
process  are  the  same."  The  instinct  does  not  appear  in  per- 
fection at  first,  for  the  same  author  notices  that  it  takes  a 
young  worker  about  three  times  as  long  to  feed  the  larvae  as 
the  female  requires,  and  that  a  great  deal  of  time  is  lost  by 
the  new  worker  "  in  poking  its  head  into  the  wrong  cells 
and  running  unnecessarily  about  over  the  face  of  the  nest." 


FIG.  41.  Paper-Making  Wasp  and  Nest.    Natural  size 

The  workers  surely  do  not  appreciate  the  character  of  their 
task,  for  the  observer  just  quoted  has  seen  a  young  worker 
gnaw  a  piece  out  of  the  body  of  a  dead  larva  and  offer  it  as 
food  to  the  mouth  of  the  same  larva;  and,  she  continues, 
"  I  once  observed  a  neuter  attack  a  live  larva,  and  after  she 
had  cut  out  and  crushed  a  fair-sized  piece  of  its  body,  come 
back  eight  times  in  the  course  of  her  examination  of  the 
cells  of  the  nest,  to  this  larva,  which  naturally  had  died  in 
the  operation,  and  offer  it  this  part  of  its  own  body,  with  the 
evident  expectation  that  it  would  be  seized  and  eaten.  .The 
eighth  time  she  dropped  the  piece  on  the  face  of  the  dead 
larva  and  went  away  with  an  air  of  '  duty  well  done '  which 
was  comical  to  behold." 


68  GENERAL  ZOOLOGY 

From  the  time  the  workers  take  up  the  tasks  of  the  nest 
the  female  is  left  free  to  devote  all  her  energies  to  laying 
eggs,  and  the  nest  is  rapidly  made  larger  by  the  workers. 
Toward  September  males  and  females  appear  from  the  cells, 
which  up  to  this  time  have  produced  only  workers.  The  males 
die  soon  after  mating.  On  the  approach  of  cold  weather,  the 
workers  also  die,  and  only  females  remain  to  hibernate  and 
begin  a  new  nest  the  next  spring. 

Another  type  of  nest,  in  which  the  horizontal  layers  are 
inclosed  in  a  thin  envelope,  is  made  by  the  somewhat  larger 
and  stouter-bodied  wasps  (Ves'pa,  Fig.  45)  commonly  known  as 
"  hornets."  These  wasps  are  generally  conspicuously  marked 
with  yellow,  and  their  nests  may  be  a  foot  and  a  half  in 
diameter. 

The  social  wasps  are  the  original  paper-makers  of  the  world. 
The  first  suggestion  as  to  the  manufacture  of  paper  by  man 
may  have  come  from  watching  the  work  of  these  insects, 
though  the  necessary  steps  may  well  have  been  taken  without 
such  suggestion,  as  the  use  of  the  leaves  of  palms  and  the 
bark  of  several  trees  is  still  common  in  China  and  India.  It 
is  interesting  to  note  that  though  the  wasps  were  the  original 
inventors  of  paper,  they  have,  in  some  cases,  learned  to  take 
advantage  of  man's  present  greater  facilities  for  its  manufac- 
ture, thus  saving  themselves  the  trouble.  In  one  case  in 
Missouri  the  wasps  found  the  damp  paper  of  bags,  which 
had  been  tied  over  grape-clusters  in  a  vineyard  to  keep  out 
injurious  insects,  so  much  to  their  liking  that  they  used  it 
freely  instead  of  their  own  wood-pulp  paper. 

Solitary  Wasps.  Those  wasps  which  are  solitary  in  habit 
make  nests  in  various  situations  and  of  different  materials, 
and  store  them  with  food,  generally  insects  and  spiders,  which 
they  often  sting  so  as  to  paralyze  but  not  to  kill  them.  Each 
species  has  its  own  method  of  providing  food,  and  each  keeps 
pretty  closely  to  the  same  material  for  nest-building.  Thus 


THE  ANTS,   BEES,  AND  WASPS 


69 


the  common  mud-dauber  (Pelopce'ua,  Fig.  42),  seen  flying 
about  on  sunny  days  over  the  muddy  edges  of  puddles  and 
pools,  builds  its  nests  of  clay  and  provisions  them  with 
spiders.  Each  cell  is  filled  with  paralyzed  spiders ;  on  top 


FIG.  42.   Mud-Dauber  and  Nest.    Natural  size 

one  egg  is  laid  and  the  cell  is  sealed.  When  the  larva  hatches 
it  finds  the  requisite  amount  of  food  to  carry  it  to  the  pupal 
stage.  These  wasps  are  distinguished  by  the  long  pedicel,  or 
stalk,  joining  the  thorax  to  the  abdomen. 

The  digger-wasps  of  the  West,  which  belong  to  the  genus 
Ammoph'ila  (Fig.  43),  make  holes  a  little  over  a  centimeter 


TO  GENERAL   ZOOLOGY 

(about  half  an  inch)  in  diameter  and  two  or  three  centimeters 
deep,  in  the  hard,  sun-baked  earth,  often  choosing  a  place 
beneath  the  protection  of  the  leaf  of  some  plant.  These  holes 
they  provision  with  caterpillars,  which  they  sting  in  several 


FIG.  43.   Digger- Wasp  using  Pebble.    Enlarged 
(From  Peckham's  The  Solitary  Waspa) 

places  till  they  are  paralyzed.  In  the  process  of  provisioning 
the  nest  some  species  close  the  opening  with  a  pellet  of 
earth  or  with  small  stones,  which  they  remove  when  they 
return  with  a  new  caterpillar.  Dr.  and  Mrs.  Peckham,  who 
have  studied  these  insects  very  carefully,  say  that  this  is, 
however,  not  an  invariable  habit,  some  individuals  leaving 
the  nest  open  while  searching  for  more  caterpillars.  These 
authors  have  this  to  say  of  the  habits  of  one  of  these 
insects. 

"  Just  here  must  be  told  the  story  of  one  little  wasp  whose 
individuality  stands  out  in  our  minds  more  distinctly  than 
that  of  any  of  the  others.  We  remember  her  as  the  most 
fastidious  and  perfect  little  worker  of  the  whole  season,  so 


THE  ANTS,   BEES,  AND   WASPS 


71 


nice  was  she  in  her  adaptation  of  means  to  ends,  so  busy 
and  contented  in  her  labor  of  love,  and  so  pretty  in  her  pride 
over  her  completed  work.  In  rilling  up  her  nest  she  put 
her  head  down  into  it  and  bit  away  the  loose  earth  from  the 
sides,  letting  it  fall  to  the  bottom  of  the  burrow,  and  then, 
after  a  quantity  had  accumulated,  jammed  it  down  with  her 
head.  Earth  was  then  brought  from  the  outside  and  pressed 
in,  and  then  more  was  bitten  from  the  sides.  When,  at  last, 
the  filling  was  level  with  the  ground,  she  brought  a  quantity 
of  fine  grains  of  dirt  to  the  spot,  and,  picking  up  a  small 
pebble  in  her  mandibles,  used  it  as  a  hammer  in  pounding 
them  down  with  rapid  strokes,  thus 
making  this  spot  as  hard  and  firm  as 
the  surrounding  surface.  Before  we 
could  recover  from  our  astonishment 
at  this  performance  she  dropped  her 
stone  and  was  bringing  more  earth. 
We  then  threw  ourselves  down  on  the 
ground,  that  not  a  motion  might  be 
lost,  and  in  a  moment  we  saw  her  pick 
up  the  pebble  and  again  pound  the 
earth  into  place  with  it,  hammering 
now  here  and  now  there,  until  all  was 
level.  Once  more  the  whole  process 
was  repeated,  and  then  the  little  crea- 
ture, all  unconscious  of  the  commotion 
that  she  had  aroused  in  our  minds,  un- 
conscious, indeed,  of  our  very  existence, 
and  intent  only  on  doing  her  work  and 
doing  it  well,  gave  one  final  comprehen- 
sive glance  around  and  flew  away." 

A  common  North  American  species  of  solitary  wasp 
(Eume'nes  frater'nus,  Fig.  44)  builds  a  pretty  little  jug- 
shaped  nest  of  clay  or  mud,  which  it  attaches  to  vegetation 


FIG.  44.  Mason- Wasp  and 

Nest.   Natural  size 


72  GENERAL  ZOOLOGY 

and  provisions  with  caterpillars.  The  young,  when  full- 
grown,  escape  through  a  hole  which  they  cut  in  the  side  of 
the  nest,  as  shown  in  the  figure. 

The  Honey-Bee.  The  life-history  of  the  honey-bee  (A' pis 
mellif'ica,  Fig.  45)  has  been  quite  well  understood  for  a  long 
time.  This  insect  offers  a  most  interesting  illustration  of  a 
society  all  the  members  of  which  act  together  for  the  good 
of  the  community.  In  their  community  specialization  of  work 
has  been  developed  to  a  remarkable  extent.  The  honey-bee, 
originally  a  native  of  the  eastern  hemisphere,  possibly  from 
the  region  along  the  eastern  shore  of  the  Mediterranean  Sea, 
has  been  domesticated  from  very  early  times  for  the  sake  of 
its  two  important  products,  honey  and  wax.  Escaped  swarms 
in  this  country  have  become  the  wild  honey-bees,  which  nest 
in  hollow  trees.  In  early  summer  a  bee  community  in  good 
condition  may  contain  from  twenty-five  to  thirty-five  thousand 
workers,  several  hundred  males,  called  drones,  but  only  one 
female,  called  the  queen  bee.  The  queen  bee  may  be  distin- 
guished from  the  workers  and  drones  by  her  larger  size ;  the 
drones  are  stouter  than  the  workers. 

Upon  the  workers  devolves  most  of  the  labor  in  connection 
with  the  life  of  the  community.  They  secrete  the  wax  and 
fashion  it  into  the  cells  of  which  the  home  is  composed.  , 
They  bring  water  to  the  hives.  They  collect  nectar  from 
flowers  and  later  regurgitate  it  and  ripen  it  into  honey  ;  they 
bring  pollen  to  mix  with  nectar  to  make  "  bee-bread,"  and 
gather  propolis,  a  gummy  substance  from  the  bud-scales  of 
certain  trees,  especially  the  poplar,  for  filling  crevices  and 
covering  foreign  objects  which  are  too. big  to  remove  from 
the  nest.  When  the  young  are  hatched  the  workers  act  as 
nurses  and  housekeepers  for  the  community,  feeding  the 
young  and  keeping  the  hive  free  from  all  substance  which 
might  decay.  In  warm  weather  some  of  them  may  be  seen 
at  the  entrance  and  along  the  passageway,  keeping  the  air  in 


THE  ANTS,  BEES,  AND  WASPS  73 

motion  with  their  wings,  thus  setting  up  a  current  which 
provides  air  and  helps  ripen  the  honey  by  evaporating  the 
water  in  it.  Finally,  as  every  one  knows,  they  are  the  defend- 
ers of  the  hive,  and  by  their  great  numbers  and  formidable 
stings  they  constitute  a  body-guard  of  no  mean  pretensions. 

The  name  "  queen  bee  "  is  misleading,  if  it  suggests  any  con- 
trol or  management  of  the  affairs  of  the  hive.  She  is  carefully 
guarded  by  the  workers,  but  that  is  on  account  of  her  impor- 
tance to  them  as  the  only  fertile  female  in  the  community, 
though  they  can,  as  we  shall  see,  produce  other  queens  from 
eggs  which  were  destined  for  workers,  if  necessity  arises.  As 
far  as  having  any  power  to  rule  is  concerned,  she  is,  in  reality, 
ruled  by  the  workers.  It  is  her  function  to  lay  the  eggs  from 
which  all  the  other  members  develop.  Those  eggs  destined 
to  become  workers  are  laid  in  cells  of  ordinary  size ;  those 
which  are  to  become  males  are  placed  in  slightly  larger  cells  ; 
while  those  which  are  to  become  queens,  though  differing  in 
no  way  at  first  from  those  which  produce  workers,  are  placed 
in  special  "  royal "  cells,  much  larger  and  of  an  irregular 
shape.  They  are,  of  course,  few  in  number  compared  with 
the  others. 

When  the  eggs  hatch,  all  the  larvae  are  fed  for  several 
days  on  a  jelly-like  substance  consisting  of  regurgitated 
food  mixed  with  a  secretion  from  glands  in  the  heads  of 
the  workers  and  poured  out  from  their  mouths.  After  this 
the  workers  and  males  receive  "bee-bread,"  a  mixture  of 
pollen  and  honey,  while  the  young  queens  are  continued  on 
their  diet  of  elaborated  material,  "  royal  jelly,"  furnished  by 
the  workers.  When  for  any  reason  a  hive  loses  its  queen,  the 
workers  proceed  to  break  down  the  walls  between  three  adja- 
cent cells  containing  worker  larvse,  kill  two  of  the  occupants, 
and  bring  the  third  to  maturity  as  a  queen  by  the  use  of  royal 
jelly.  The  first  eggs  laid  in  the  spring  produce  workers  ;  the 
males  are  produced  from  unfertilized  eggs  laid  by  the  queen. 


74  GENERAL  ZOOLOGY 

When  the  larva  is  full  grown  no  more  food  is  supplied  to  it 
and  the  cell  is  sealed  with  a  waxen  cover.  Within  this  prison 
the  larva  spins  a  cocoon  and  changes  to  a  pupa.  Within  three 
weeks  from  the  laying  of  the  egg  the  worker  bee  cuts  a  hole 
in  the  covering  of  its  cell  and  emerges.  A  queen  is  produced 
in  somewhat  less  time ;  a  drone  requires  slightly  longer. 

In  late  spring  or  early  summer,  as  the  colony  has  increased 
in  size,  the  time  approaches  for  one  of  the  new  queens  to 
appear  from  the  pupal  stage.  A  peculiar  noise  may  be  heard, 
made  probably  by  the  wings  of  the  imprisoned  queen.  Part 
of  the  ordinary  work  of  the  hive  is  neglected,  and  the  old 
queen  rushes  forth  with  a  large  number  of  the  community, 
generally  alighting  in  a  palpitating  mass  on  some  near-by 
tree  or  other  support.  This  is  the  "  swarming"  of  the  bees. 
If  provided  with  a  new  hive,  they  will  generally  settle  down 
quietly  in  their  new  home.  Bees  are  particular  as  to  the* 
state  of  the  weather  at  the  time  of  swarming,  appearing  only 
when  the  sky  is  clear.  The  workers  carry  a  store  of  honey 
in  their  crops,  as  if  prepared  for  a  long  trip,  which  in  a  state 
of  nature  may  often  have  occurred  before  the  bees  could  find 
a  hollow  tree  or  crevice  among  rocks  suitable  for  a  home. 
The  swarming  serves  the  purpose  of  lessening  the  chances 
of  a  total  extinction  of  the  species,  by  increasing  the  number 
of  communities. 

Meanwhile  the  new  queen  appears  in  the  old  hive,  and 
after  a  flight  in  the  'air  with  the  drones,  during  which  ferti- 
lization occurs,  she  settles  down  to  her  duty  of  egg-laying. 
This  flight  and  the  swarming  are  the  only  occasions  upon 
which  the  queen  leaves  the  hive.  The.  number  of  swarms 
thus  given  off  varies  with  the  size  of  the  original  community, 
and  seems  to  depend  somewhat  on  climatic  conditions.  It  is 
not  uncommon  to  have  three  swarms  in  a  season.  When  the 
community  is  to  send  out  no  more  swarms,  the  queen  is  per- 
mitted to  sting  the  other  young  queens  to  death.  If  by  any 


THE  ANTS,   BEES,  AND  WASPS  T5 

chance  two  queens  meet,  a  conflict  begins  at  once,  and  the 
usual  result  is  the  death  of  one  of  them.  This  is  often  spoken 
of  as  due  to  the  jealousy  of  the  queens,  but  it  may  have  a 
meaning  in  connection  with  the  necessity  the  community  is 
under  of  sending  out  swarms  to  maintain  a  separate  existence. 
The  sting  of  the  queen  is  used  only  in  these  battles  and 
in  slaying  the  young  queens.  At  the  end  of  the  swarming 
season  the  workers  set  upon  the  drones  and  kill  them,  casting 
their  dead  bodies  out  of  the  hive.  The  queens  live  for  several 
years,  depositing  two  or  three  thousand  eggs  a  day  during  a 
part  of  the  season.  The  workers  live,  as  a  rule,  less  than  two 
months. 

The  wax  of  which  the  cells  of  the  comb  are  composed  is 
secreted  in  the  form  of  thin  plates  in  "  wax-pockets  "  beneath 
some  of  the  abdominal  somites.  While  preparing  this,  full- 
fed  workers  hang  motionless  to  the  cells  in  the  upper  part  of 
the  hive,  and  in  about  twenty-four  hours  the  wax  appears. 
This  is  removed  by  other  workers  and  is  used  in  construc- 
tion. Honey  is  made  for  food  for  the  young  and  for  winter 
consumption  of  the  colony.  The  pollen  of  flowers  is  brought 
to  the  hive  in  "  pollen-baskets,"  clear  spaces  surrounded  by 
hairs  on  the  outer  side  of  the  hind  tibiae.  The  basal  joints  of 
the  hind  tarsi  are  much  enlarged,  and  are  used  as  brushes 
to  gather  the  pollen. 

Bumblebees  and  Guest-Bees.  The  bumblebees  (Bom'bus, 
Fig.  45)  are  social  bees,  having  homes  in  fields,  in  deserted 
mouse-nests  and  similar  places.  The  nest  is  begun  early  in 
the  spring  by  a  female  which  has  wintered,  and,  as  with  the 
social  wasps,  the  burdens  of  the  home  are  turned  over  to  the 
young  workers  when  they  emerge.  Late  in  the  season  other 
females  and  males  appear,  but  there  is  no  swarming  as  with 
the  honey-bee.  On  the  approach  of  cold  weather  the  workers 
and  males  die.  The  honey  made  is  strong-smelling,  but  much 
sought  after  by  boys  in  the  country,  perhaps  as  much  for  the 


76 


GENERAL  ZOOLOGY 


danger  connected  with  its  capture  as  for  the  sake  of  the  honey 
itself.  Boys  in  the  West  rob  the  bees  by  placing  a  gallon  jug 
partially  filled  with  water  in  the  vicinity  of  the  nest  and 
thoroughly  arousing  the  members  of  the  community.  The 
boys  make  good  their  escape  to  a  safe  distance,  and  the  bees, 
perceiving  the  jug,  fly  to  its  open  mouth,  which  echoes  the 
buzzing  of  their  wings.  Angered  by  the  sound,  some  bees  fly 

Mimicked  Forms,  —  Insects  with  means  of  defense 
The  honey-bee  A  wasp  A  bumblebee 

(Apis  mellifica)  (Vespa  occidentalis)  (lloinbus  Howardii) 


Mimicking  Forms,  —  Insects  without  means  of  defense 
A  fly  A  beetle  A  fly 

(Eristalis  latifrons)          (Clytus  niurginicollis)  (Vohicella  evecta) 


FIG.  45.   Mimicked  and  Mimicking  Insects.     Natural  size. 

From  photographs 
(From  Hunter's  Studies  in  Insect  Life) 

into  the  mouth  of  the  jug,  thus  adding  to  the  noise  and 
attracting  others.  It  is  said  that  with  two  disturbances  of  the 
nest  the  worker  bees  can  all  be  captured. 

There  are  several  bees  called  guest-bees  (Psith'yrus),  which 
live  in  the  nest  of  the  bumblebees,  apparently  on  good  terms 


THE  ANTS,   BEES,  AND   WASPS 


77 


with  them,  though  they  do  not,  so  far  as  known,  perform 
any  useful  function.  Their  eggs  are  laid  with  the  eggs  of 
the  bumblebees,  and  the  larvae  feed  on  the  food  which  the 
bumblebees  provide  for  their  own  young.  Some  of  the  guest- 
bees  resemble  their  hosts  quite  closely  ;  others  are  different 
in  appearance,  so  that  it  cannot  be  said  in  all  cases  that  the 
bumblebees  are  deceived  by  the  resemblance.  One  effect  of 


•'•- 


FIG.  46.  Leaf-Cutter 
Bee  and  Nest. 
Natural  size 


the  dependence  of 
the  guest -bees  on 
their  hosts  is  seen 
in  the  absence  from 
the  hind  legs  of 
the  former  of  the 
pollen-collecting 
and  pollen-carrying 
organs,  which  have 
probably  been  lost  through  disuse.  It  has  been  observed  that 
the  bumblebees  sometimes  resent  the  introduction  of  one  of 
the  guest-bees  into  their  nest,  though  they  may  later  become 
accustomed  to  it  and  make  no  further  trouble. 

Solitary  Bees.  There  are  solitary  bees,  just  as  there  are 
solitary  wasps.  Their  habits  are  very  diverse ;  some  make 
nests  of  mud  or  dig  tunnels  in  the  ground ;  some  are  car- 
penters, boring  into  wood  ;  and  others  are  leaf-cutters,  taking 
circular  pieces  out  of  leaves,  which  they  use  to  line  their 


78  GENERAL  ZOOLOGY 

nests.  Fig.  46  represents  the  work  of  one  species,  the  leaf- 
cutter  bee  (Megachi'le  acu'ta),  which  makes  long  tunnels  in 
wood  or  in  the  ground.  The  eggs  are  laid  singly  on  a  paste 
of  nectar  and  pollen,  which  is  placed  carefully  in  a  leaf-lined 
cell  and  covered  with  a  circular  lid.  Several  such  cells  are 
generally  to  be  found  in  one  nest. 

Ants.  Ants  have  long  been  considered  models  of  industry. 
In  many  respects  some  of  the  features  of  their  life-history 
are  the  most  remarkable  of  anything  in  the  insect-world.  So 
specialized  have  the  members  of  the  community  become  in 
some  cases  that  there  are  not  only  males  and  females,  but 
large  and  small  workers  (workers  major  and  minor),  and 
soldiers  for  the  defense  of  the  colony.  Ants  build  nests  in 
the  ground,  piling  up  the  material  taken  out  for  their  bur- 
rows in  the  characteristic  ant-hills ;  or  they  make  tunnels 
in  wood.  Some  inhabit  the  interior  of  thorns  or  the  hollow 
stems  of  grasses  ;  others  live  on  certain  trees,  from  which 
they  obtain  all  their  food,  forming  a  kind  of  body-guard  by 
defending  the  tree  from  the  attacks  of  various  enemies.  The 
food  of  ants  is  both  animal  and  vegetable,  the  former  consist- 
ing of  other  insects,  the  latter  of  plant  fluids.  They  are  also 
extremely  fond  of  the  sweet  substance  called  "  honeydew," 
furnished  by  the  aphids  and  some  few  other  insects. 

The  eggs  are,  of  course,  extremely  minute,  and  hatch  into 
footless  larvao,  which  resemble  those  of  the  bees  and  wasps. 
The  workers  take  great  care  of  the  young,  feeding  them 
and  moving  them  about  in  conformity  with  changes  in  tem- 
perature and  amount  of  moisture.  Among  ants  generally, 
the  workers  feed  not  only  the  young  but  even  give  up  food 
to  each  other,  when  this  is  demanded  by  a  stroke  of  the  an- 
tennae. The  pupal  stage  is  generally  passed  in  silken  cocoons. 
These  are  the  so-called  "  ant-eggs,"  which  are  the  objects  of 
much  solicitude  when  a  nest  is  exposed.  The  imagoes  are 
unable  to  escape  from  the  pupal  case  without  the  help  of  the 


THE  ANTS,   BEES,  AND  WASPS  T9 

workers.  The  males  and  females  are  at  first  winged,  and 
take  flight  in  great  numbers  into  the  air  on  some  warm  day 
in  spring.  At  this  time  fertilization  occurs.  On  their  return 
the  males  soon  die,  and  the  females,  stripping  off  their  wings, 
become  the  mothers  of  colonies.  The  females  can  be  distin- 
guished from  the  workers  by  their  larger  size  and  the  presence 
of  well-developed  ocelli. 

Many  other  insects,  especially  beetles,  live  habitually  in  the 
nests  of  ants,  and,  in  some  cases  at  least,  seem  to  perform  some 
useful  function,  —  acting  as  scavengers,  for  instance.  These 
cases,  like  that  of  the  bumblebees  and  guest-bees,  may  be 
cited  as  illustrations  of  commensalism  (Lat.  com  ( =  cum\  to- 
gether ;  mensa,  table),  an  association  of  one  species  of  animal 
with  another  for  support  or  advantage,  but  not  as  a  parasite. 

An  illustration  of  cooperation  between  two  different  species 
of  animals  is  shown  in  certain  ants  and  aphids.  The  corn-louse 
ant '(La'sius)  collects  the  eggs  and  young  of  a  species  of  aphid 
(A'plds  mai'dis),  which  attacks  the  roots  of  corn  in  the  Middle 
States,  and  guards  them  throughout  the  winter  in  subterra- 
nean burrows,  so  as  to  provide  a  constant  supply  of  "  honey- 
dew."  Some  ants  build  a  shelter  of  wood-pulp  or  mud  over 
colonies  of  aphids,  which  are  crowded  on  a  branch,  from  which 
they  derive  their  nourishment.  These  aphids  are  often  spoken 
of  as  the  cows  of  the  ants.  In  these  cases  the  relation  between 
the  ants  and  aphids  is  clearly  of  a  more  intimate  character 
than  the  association  of  the  bumblebees  and  guest-bees;  and 
the  advantages  are  mutual,  for  while  the  ants  secure  a  con- 
stant supply  of  food,  the  aphids  receive  care  and  a  certain 
amount  of  protection  against  their  enemies.  This  association 
is  spoken  of  as  symbiosis  (Gr.  syn,  together  ;  bios,  life). 

An  ant  found  in  eastern  Asia  lives  in  shelters  which  it 
forms  on  the  leaves  of  trees  by  fastening  the  edges  of  the 
leaves  together.  The  imagoes  have  no  sticky  secretion  for 
this  work,  but  the  larvse  have  glands  which  furnish  such  a 


80 


GENERAL  ZOOLOGY 


secretion  for  the  purpose  of  spinning  their  cocoons.  The 
imagoes  seize  the  larvae  in  their  jaws,  rubbing  them  backward 
and  forward  over  the  edges  of  the  leaves,  when  the  sticky 


FIG.  47.  Tunnels  of  a  Mexican  Blind  Ant 

secretion  is  poured  out  and  the  edges  of  the  leaves  are  drawn 
together  and  kept  there. 

Fig.  47  shows  the  tunnels  of  a  species  of  blind  ant  from 
Mexico,  on  the  trunk  of  a  "wild  fig."  The  tunnels  serve  as  a 
safe  means  of  communication  between  the  nest  underground 
and  the  leaves  of  the  tree. 

The  honey-ant  of  Texas  (Myrmecocys'tus  mel'liger)  has  one 
set  of  workers  peculiarly  modified  to  act  as  storage  vessels 
for  sweets.  The  abdomens  of  these  are  distended  with  a  store 
of  grape-sugar,  till  they  are  as  large  as  a  currant.  These 
workers  cling  to  the  roof  of  the  nest,  and  in  times  of  famine 
can  be  drawn  upon  for  food  by  the  other  workers. 


THE  ANTS,   BEES,  AND   WASPS 


81 


The  agricultural  ant  (Myrmi'ca  molefac'iens),  of  the  same 
region,  clears  large  spaces,  often  several  feet  in  diameter, 
cutting  down  all  vegetation  growing  thereon,  and  rears  a 
grain-bearing  grass,  storing  its  seeds  in  subterranean  chambers. 
Several  kinds  of  ants  have  the  habit  of  attacking  other  kinds 
and  carrying  off  their  pupse.  In  one  (Formi'ca  sanguin'ea),  a 
small  reddish  species,  the  habit  has  become  firmly  fixed,  and 
periodical  raids  are  made  upon  a  larger  black  species,  which 
are  afterwards  raised  in  the  nests  of  their  captors.  One  ant 
of  a  slave-making  tendency,  found  in  Europe  (Polyer'gus 
rufes'cens),  has  carried  the  habit  so  far  that  it  has  lost  the 
power  of  feeding  and  taking  care  of  itself,  depending  entirely 
on  the  exertions  of  its  servants.  The  wars  of  ants  have  been 
known  for  a  long  time,  and  many  accounts  are  extant  of  the 
fierceness  of  the  struggle  between  opposing  armies. 

Gall-Flies  and  Ichneumon-Flies.  The  gall-flies  form  many 
of  the  swellings  on  plants,  known  as  galls.  A  common  gall- 
fly of  the  oak 
(Amphib'olips) 
is  shown  in  Fig. 
48.  The  gall  is 
caused  by  the 
female  laying 
an  egg  in  the 
leaf- tissue, 
which  swells  up 
when  the  larva 
hatches,  owing, 

perhaps,  to   the 

FIG.  48.  Gall-Fly .    Natural  size 
presence  of  some 

irritating  substance.  The  young  feed  on  the  material  of  the 
gall  until  they  are  ready  to  go  into  the  pupal  stage.  Many 
of  these  galls  harbor  also  guest  gall-flies,  living  with  the 
others  as  commensals. 


GENERAL  ZOOLOGY 

Closely  allied  to  the  gall-flies  are  the  ichneumon-flies,  one 
of  which,  O'phion,  is  shown  in  Fig.  49.  This  species  deposits 
its  eggs  in  the  burrows  of  a  wood-boring  larva  by  means  of  its 
long  ovipositor,  and  the  ichneumon  larva  on  hatching  moves 
along  in  its  burrow  until  it  finds  its  host,  when  it  fastens 
itself  to  it  and  destroys  it  by  sucking  its  blood.  This  carniv- 
orous habit  may  be  regarded  as  an  approach  to  parasitism. 
Many  of  the  ichneumon-flies  are  true  parasites  in  the  larval 
stage,  the  eggs  being  deposited  on  the  skin  or  in  the  body 


FIG.  49.    Ichneumon-Fly.    Natural  size 

of  the  caterpillars,  upon  the  fluids  of  which  the  ichneumon 
larva  feeds.  The  pupal  stage  is  generally  passed  within  the 
body  of  its  victim. 

Saw-Flies.  The  saw-flies  differ  from  all  the  insects  so  far 
discussed  in  this  chapter  in  having  the  base  of  the  abdomen 
as  broad  as  the  thorax.  The  ovipositor  of  the  female  consists 
of  a  pair  of  saws,  which  are  used  to  make  slits  in  the  leaves 
and  stems  of  plants,  in  which  she  deposits  her  eggs.  Fig.  50 
shows  the  American  saw-fly  (Cim'bex  america! no) ,  our  largest 
species.  The  larva  looks  like  the  caterpillar  of  a  butterfly  or 
moth,  but  has  more  legs.  It  has  the  curious  habit  of  coiling 
the  posterior  end  of  its  body  about  a  branch,  as  shown  in  the 
illustration.  It  forms  a  brown  cocoon  in  which  the  winter  is 
passed  in  the  ground.  An  Australian  saw-fly  is  credited  with 
staying  with  its  eggs  till  they  hatch,  afterwards  brooding  over 
the  young  with  outstretched  legs,  and  protecting  them  by  all 
the  means  in  her  power. 


THE  ANTS,   BEES,   AND   WASPS 


83 


Definition  of  Hymenoptera  (Gr.  hymen,  membrane ;  pteron, 
wing).  The  insects  which  we  have  been  considering  in  this 
chapter  all  agree  in  possessing  mouth-parts  adapted  both  to 


FIG.  50.  Metamorphosis  of  Saw-Fly.    Natural  size 

biting  and  lapping,  and  four  membranous  wings  with  few 
veins.  The  order  is  called  Hymenop'tera.  A  structural  pecul- 
iarity is  the  union  of  the  first  abdominal  somite  to  the  thorax, 
so  tl]^t  the  division  between  what  appears  to  be  the  thorax 
and  the  abdomen  comes  after  the  first  abdominal  somite. 
The  Hymenoptera  undergo  "  complete  "  metamorphosis.  The 
larvse  are  called  maggots. 


CHAPTER  IX 
THE  INSECTS :  HEXAPODA 

Though  numberless  these  insect  tribes  of  air, 
Though  numberless  each  tribe  and  species  fair, 
Who  wing  the  moon,  and  brighten  in  the  blaze, 
Innumerous  as  the  sands  which  bend  the  seas  ; 
These  have  their  organs,  arts,  and  arms,  and  tools, 
And  functions  exercised  by  various  rules. 

H.  BROOKE,  Universal  Beauty. 

Definition  of  Hexapoda  (Gr.  hex,  six;  pom  ('pod),  foot). 
The  previous  chapters  have  been  devoted  to  entomology,  that 
branch  of  zoology  which  treats  of  insects.  The  insects  belong 
to  the  class  Hexap'oda,  the  most  numerous  of  all  classes 
of  animals,  comprising  four  fifths  of  the  animal  kingdom. 
Insects  are  built  externally  upon  the  plan  of  a  series  of 
somites,  grouped  in  three  regions  and  with  segmented  ap- 
pendages on  two  of  them,  —  the  head  and  thorax.  Except 
in  very  few  cases,  where  this  number  is  reduced,  the  imagoes 
have  six  legs.  Hexapods  are  found  in  every  variety  of  situa- 
tion, though  they  are,  as  a  whole,  adapted  to  life  on  the  land 
and  in  the  air.  A  system  of  tracheae  is  universally  present 
in  the  imagoes,  though  the  young  of  some  species  have  tra- 
cheal  gills  for  breathing  in  the  water. 

The  hard  chitinous  covering  (exoskeleton)  necessitates  fre- 
quent molts  to  provide  for  increase  in  size.  The  molts  may 
or  may  not  be  accompanied  by  metamorphosis.  The  most 
marked  change  of  form  is  seen  in  the  Coleoptera,  Lepidop- 
tera,  Hymenoptera,  and  Diptera.  In  the  first  three  of  these 
orders,  and  in  some  Diptera,  while  the  change  in  external 
form  is  often  considerable,  most  of  the  larval  organs  persist 

84 


THE  INSECTS:   HEXAPODA  85 

in  the  imago,  even  though  they  undergo  considerable  modi- 
fication in  the  process  of  transformation.  In  that  division  of 
the  Diptera  represented  in  our  account  of  the  order  by  the 
house-flies,  flesh-flies,  bot-flies,  and  hover-flies,  the  change  from 
the  larva  to  imago  is  so  complete  that  nearly  all  the  larval 
organs  are  disintegrated  and  the  organs  of  the  imago  are 
built  from  separate  masses  of  cells  (imaginal  disks  or  buds) 
which  alone  escape  destruction.  The  breaking-down  of  the 
larval  tissues  is  due  to  the  activity  of  certain  white  blood-cells 
called  phagocytes  (voracious  cells).  It  has  been  suggested  that 
the  escape  of  the  imaginal  disks  from  the  general  destruction 
is  due  to  the  fact  that  these  masses  of  cells  alone  remain  func- 
tional during  the  transition  period  between  larva  and  imago. 

All  through  the  class  a  division  of  labor  has  been  reached, 
in  which  the  young  feed  and  build  up  the  material  for  the 
imagoes,  which  reproduce  the  species. 

Instinct  and  Intelligence  in  Insects.  Some  of  the  most  inter- 
esting questions  in  zoology  are  those  dealing  with  the  various 
reactions  of  animals  to  external  objects,  —  the  general  sub- 
ject of  the  behavior  of  animals.  Some  actions  we  explain  as 
due  to  instinct,  others  we  say  are  accompanied  by  intelligence, 
and  still  others  we  believe  to  be  governed  by  reason.  There 
is  the  widest  possible  difference  of  opinion  among  naturalists 
as  to  the  relative  importance  of  each  of  these  in  the  life  of 
the  lower  animals.  Indeed,  there  is  as  yet  little  uniformity 
in  the  definition  of  the  terms  themselves,  so  that  in  our  dis- 
cussion of  this  subject  in  the  class  of  insects  we  shall  follow 
Professor  Lloyd  Morgan,  of  England,  in  his  book,  Animal 
Behavior,  by  defining  as  instinctive  those  acts  which  are  simi- 
larly performed  by  all  the  members  of  a  group  of  animals ; 
which  are,  on  their  first  occurrence,  independent  of  experi- 
ence ;  and  which  tend,  usually,  to  the  well-being  of  the 
individual  and  the  preservation  of  the  race.  The  act  of  the 
newly  hatched  larva  of  the  milkweed-butterfly  in  devouring 


86  GENERAL  ZOOLOGY 

its  egg-shell  would  therefore  be  called  instinctive,  as  would 
the  behavior  of  Pronuba  in  pollinating  the  yucca. 

Dr.  and  Mrs.  Peckham,  in  their  work,  The  Solitary  Wdsps, 
from  which  we  have  quoted  before,  enumerate  eight  primary 
instincts : 

1.  Stinging. 

2.  Taking  a  particular  kind  of  food. 

3.  Method  of  attacking  and  capturing  prey. 

4.  Method  of  carrying  prey. 

5.  Preparing  nest  and  capturing  prey,  or  the  reverse. 

6.  The  mode  of  taking  prey  into  the  nest. 

7.  The  general  style  or  locality  of  nest. 

8.  The  spinning  or  not  spinning  of  a  cocoon,  and  its  specific  form 
when  made. 

Some  instincts  seem  to  be  little  more  than  direct  responses 
of  the  nervous  system  of  the  animal  to  external  exciting 
causes  (see  paragraph  011  reflex  action,  Chapter  XVI,  p.  208). 
Thus  it  is  well  known  that  moths  and  some  other  night-flying 
insects  show  a  positive  reaction  toward  light,  which,  under 
certain  conditions,  may  tend  toward  the  destruction  of  the 
insects,  as  may  be  seen  about  electric  arc-lights  in  city  parks 
in  summer.  The  blow-fly  is  attracted  to  the  decaying  meat 
in  which  it  lays  its  eggs  by  the  chemical  substances  given 
off,  which  are  perceived  by  the  fly's  sense  of  smell.  Experi- 
ments on  certain  caterpillars  seem  to  show  that  their  life  is 
largely  determined  by  their  positive  reaction  to  light,  their 
negative  reaction  to  gravity,  —  these  two  combining  to  compel 
the  caterpillars  to  crawl  upward,  —  and  a  contact  reaction 
with  the  convex  terminal  buds,  tending  to  hold  the  cater- 
pillar in  place  when  at  the  end  of  twigs.  When  branches 
were  inverted  and  placed  in  a  receptacle  in  which  certain 
caterpillars  were,  the  latter  remained  at  the  top  of  the  twigs, 
though  food  was  only  a  few  inches  away,  showing  that  the 
caterpillars  were  not  normally  attracted  to  their  feeding-place 
at  the  ends  of  twigs  merely  by  the  presence  of  food  there. 


THE  INSECTS:    HEXAPODA  87 

Actions  which  are  due  to  the  results  of  individually 
acquired  experience,  and  which  are  performed  without  reflec- 
tion or  deliberation  as  to  the  means  to  be  employed,  or  knowl- 
edge of  the  end  to  be  reached,  are  termed  intelligent  actions 
by  Professor  Morgan.  The  behavior  of  that  particular  Ammoph- 
ila  observed  to  make  use  of  a  stone  to  pound  down  the  sand 
over  her  nest  may  be  called  intelligent,  using  the  word  in 
the  sense  just  defined.  The  power  possessed  by  the  honey-bee, 
bumblebees,  and  other  Hymenoptera,  of  finding  their  way 
back  to  the  nest,  often  from  a  considerable  distance,  may  be 
dependent  on  a  knowledge  of  the  locality  acquired  in  their 
various  trips.  If  so,  it  would  be  an  example  of  an  intelligent 
action.  Many  of  the  habits  of  ants  already  described  should 
probably  be  included  here. 

The  word  "  intelligent  "  is  commonly  used  to  cover  another 
and  quite  different  class  of  activities,  which  demand  separate 
consideration.  To  those  activities  which  are  guided  in  accord- 
ance with  a  plan  which  takes  into  consideration  both  the  ques- 
tion of  means  to  be  employed  and  the  end  to  be  reached 
Professor  Morgan  applies  the  term  "  rational."  Thus,  a  man 
in  attempting  to  cross  a  swollen  brook  will  consider  the  pos- 
sibility of  leaping,  wrading,  or  swimming  across;  or  he  will 
look  about  for  material  to  make  a  bridge,  noting  the  posi- 
tion of  stones  which  might  serve  for  supports,  and  consider- 
ing, perhaps,  the  possibility  of  piecing  together  two  short 
boards  to  make  one  board  long  enough  for  his  purpose.  When 
action  is  finally  taken  it  is  the  result  of  a  carefully  consid- 
ered plan.  An  example  of  this  class  of  actions  cannot  be 
given  from  the  insects,  as  we  have  at  present  no  satisfactory 
evidence  that  the  behavior  of  any  insect  ever  rises  to  the 
rational  plane. 

In  the  discussion  of  this  question  it  must  not  be  forgotten 
that  instincts  are  not  fixed  and  unalterable,  but  that  they  are 
constantly  being  modified  by  new  experiences.  Therefore  many 


88  GENERAL  ZOOLOGY 

of  the  actions  of  animals  should  not  be  classified  as  purely 
instinctive  or  purely  intelligent,  for  they  may  contain  elements 
of  both  factors.  The  words  "  instinctive  "  and  "  intelligent " 
can  only  be  used  to  denote  an  apparent  preponderance  of  one 
or  the  other  factor.  This  is  well  illustrated  by  the  observa- 
tion Professor  Morgan  quotes  from  M.  Fabre,  who  "  describes 
how  a  Sphex,  one  of  the  solitary  wasps,  instinctively  draws  its 
prey,  a  grasshopper,  into  the  burrow  by  its  antennae.  When 
these  were  cut  off  the  wasp  pulled  the  grasshopper  in  by  the 
jaw  appendages ;  but  when  these  were  removed  she  seemed 
incapable  of  further  accommodation  to  the  unusual  circum- 
stances." Here  we  see  not  only  obedience  to  a  strongly 
marked  instinctive  tendency,  but  also  some  power  to  modify 
the  instinctive  reaction.  It  seems  strange  to  us  that  if  the 
wasp  were  capable  of  making  this  deviation  from  her  instinc- 
tive mode  of  procedure,  she  should  not  take  the  slight  further 
step  of  seizing  upon  the  fore  legs. 

Another  caution  must  also  be  stated.  The  distinctions 
already  made  assume  that  we  are  able  to  determine  the 
mental  states  of  animals  ;  but  this  is  true  only  in  a  very  gen- 
eral way.  We  interpret  the  mental  state  of  human  beings 
by  inference  from  their  actions,  but  with  the  lower  animals 
we  have  no  positive  means  of  knowing  what  mental  state 
accompanies  any  given  action,  since  their  physical  organiza- 
tion is  so  different  from  ours.  And  not  only  is  this  true,  but 
we  also  lack  a  language  to  express  the  facts  we  observe  con- 
cerning the  mental  life  of  the  lower  animals,  since  the  words 
we  use  have  their  meaning  in  connection  with  the  facts  of 
human  psychology. 

Economic  Importance  of  Insects.  According  to  the  report 
of  the  Secretary  of  Agriculture  for  1902,  the  fixed  capital  of 
agriculture  in  the  United  States  amounted  in  1900  to  twenty 
billions  of  dollars,  or  four  times  the  amount  invested  in 
manufactures.  More  than  half  of  the  people  of  the  United 


THE  INSECTS:    HEXAPODA  89 

States  live  on  farms.  When  it  is  considered  that  our  crops 
are  attacked  not  by  one  but  often  by  many  different  insects, 
and  that,  according  to  the  estimate  of  one  of  the  state  ento- 
mologists of  New  York,  there  is  no  crop  cultivated  which 
infesting  insects  do  not  diminish  by  at  least  one  tenth,  it  is 
plain  that  the  economic  relations  of  insects  to  agriculture  are 
extremely  important.  Nearly  every  order  has  its  injurious 
forms.  Thus  the  Orthoptera  has  its  locusts ;  the  Hemiptera, 
the  plant-bugs  and  aphids;  the  Coleoptera,  the  wireworms 
and  leaf-beetles ;  the  Diptera, 
various  flies  ;  while  almost  the 
whole  army  of  the  larvae  of  the 
Lepidoptera  feed  on  plants. 

The  story  of  the  introduction 
and  spread  of  the  gypsy-moth 
of  Europe  (Porthet'ria  dis'par,  FlG.  61.  Gypsy-Moth.  Natural  size. 
Fig.  51)  in  Massachusetts,  (After  Howard,  Bulletin  No.  ll,x.s., 
teaches  an  important  lesson.  Umted  States  Department  of  Agri- 

1  culture,  Division  of  Entomology) 

This  insect,  long  well  known 

by  European  foresters  as  destructive,  was  probably  introduced 
in  1869  by  a  professor  connected  with  Harvard  Observa- 
tory, who  was  interested  in  breeding  silk-producing  insects. 
The  larvae  escaped  into  his  garden  at  Medford,  near  Boston, 
and  though  search  was  made  for  them,  not  all  were  found. 
Nothing  was  heard  from  them  for  fifteen  years,  when  they 
began  to  be  troublesome  in  gardens.  By  1889  they  had  mul- 
tiplied to  such  an  extent  that  they  attacked  every  green  thing, 
and  the  bare  branches  of  trees  in  every  direction  gave  evi- 
dence of  the  extent  of  the  devastations.  In  this  year  the 
insect  was  identified.  Up  to  that  time  it  had  been  called 
simply  "  the  caterpillar."  First  the  town  of  Medford,  and 
then  the  state,  took  up  the  matter,  and  the  first  state  appro- 
priation of  twenty-five  thousand  dollars  was  passed.  Since 
that  time  additional  appropriations  have  been  called  for,  till 


90  GENERAL  ZOOLOGY 

seven  hundred  and  seventy-five  thousand  dollars  have  been 
spent  in  a  territory  comprising  about  two  hundred  square 
miles.  The  end  is  not  yet,  for  Dr.  Howard,  chief  of  the  Divi- 
sion of  Entomology,  United  States  Department  of  Agriculture, 
in  his  report  on  The  G-ypsy  Moth  in  America,  from  whose  paper 
these  facts  have  been  taken,  says  that  appropriations  must  con- 
tinue for  several  years  in  order  to  exterminate  the  insects. 

The  Division  of  Entomology  of  the  United  States  Depart- 
ment of  Agriculture  has  been  the  means  of  saving  large  sums 
to  the  agricultural  interests  of  the  country  by  its  various 
activities,  such  as  the  importation  from  other  countries  of 
beneficial  species  and  its  study  of  the  habits  of  insects  to 
find  the  best  method  of  attack.  Many  of  the  states  maintain 
boards  of  agriculture  which  employ  entomologists. 

The  cotton-boll  weevil  (Anthon'omus  yran'dis)  has  recently 
become  a  serious  menace  to  the  cotton  industry  of  the  south- 
ern states.  The  weevils  are  beetles  possessing  a  long  snout ; 
this  organ  is  often  used  by  the  female  for  piercing  the  tissues 
of  plants  to  deposit  her  eggs.  Among  the  weevils  are  many 
formidable  enemies  of  the  farmer.  In  this  particular  case 
the  cotton  industry  has  in  some  places  been  threatened  with 
practical  extinction.  The  Division  of  Entomology  has  been 
unremitting  in  its  effort  to  find  means  to  check  the  ravages 
of  this  weevil. 

The  relations  recently  discovered  between  some  of  the 
Diptera  and  disease  must  not  be  overlooked  in  considering 
the  influence  of  insects  on  man,  outside  of  his  interests  in 
agriculture. 

Among  beneficial  insects  may  be  mentioned  the  parasitic 
ichneumon-flies  among  the  Hymenoptera,  and  the  carnivo- 
rous lady-beetles  and  many  ground-beetles  among  the  Cole- 
optera.  Comparatively  few  insects  are  directly  useful  to 
man ;  among  such  may  be  mentioned  the  silkworm,  honey- 
bee, cochineal-insect  and  lac-insect. 


THE  INSECTS:    HEXAPODA 


91 


Relations  between  Insects  and  Flowers.  In  order  to  make 
seed,  the  flowering  plants  require  to  have  the  pollen  furnished 
by  the  stamens  (Fig.  52,  1)  carried  to  the  pistil  (Fig.  52,  2)  of 
the  same  kind  of  plant.  The  pollen  is  necessary  to  the  ferti- 
lization of  the  ovule  (Fig.  52,3),  which  afterwards  grows  into 
the  seed.  Continuous  pollination  of  a  plant  by  pollen  which 
it  furnishes  from  its  own  stamens  has  been  found  to  be  detri- 
mental to  the  vigor  of  the 
seeds.  We  find  in  nature 
many  devices  to  insure 
fertilization  by  pollen 
from  another  plant  of  the 
same  kind,  that  is,  by 
cross-pollination. 


Waite,  Year-book,  United  States  Depart- 
ment of  Agriculture,  1898) 

1,  stamen;  2,  pistil;  3,  ovule 


Some  plants  have  the 
stamens  and  pistils  so 
placed  in  the  flower  that 
no  pollen  can  fall  from 
one  to  the  other;  some 
ripen  their  stamens  and 

pistils  at  different  times.  FIG.  52.  Diagram  of  Pear  Flower.  (After 
Many  have  the  stamens 
and  pistils  on  separate 
plants,  and  a  great  num- 
ber, though  the  stamens  and  pistils  are  close  together,  are 
wholly  or  partially  sterile  to  their  own  pollen,  and  "  set "  their 
seeds  only  if  the  pistils  receive  pollen  from  the  stamens  of 
another  plant  of  the  same  species.  This  is  the  case  with  many 
of  the  fruit  trees. 

The  wind  carries  pollen  for  some  plants  which  have  their 
stamens  and  pistils  more  or  less  exposed,  but  a  great  number 
of  plants,  especially  those  with  the  most  beautiful  flowers, 
depend  on  insects  to  bring  about  pollination.  So  far  has 
this  dependence  gone  that,  in  many  cases,  plants  have  become 


92 


GENERAL  ZOOLOGY 


unable  to  pollinate  themselves.  It  is  now  clear  that  the 
color,  scent,  nectar,  and  in  many  cases  the  form  of  flowers 
have  been  developed  in  connection  with  their  insect  visitors. 
The  insects  most  concerned  in  the  pollination  of  flowers  are 
flies,  butterflies,  wasps,  and  bees. 

Some  insects  visit  flowers  for  the  sake  of  the  nectar.  Pol- 
lination results  from  the  insect  brushing  itself  against  the 
pollen-bearing  organs  and  subsequently  rubbing  this  pollen 
on  to  the  pistil  in  a  neighboring  flower  in  the  search  for 
nectar.  But  the  case  of  Pronu'ba  (Fig.  53)  is  somewhat 

different.  Pronuba  is  a 
white  moth  a  little  over 
a  centimeter  (about  half 
an  inch)  long,  which 
lives  in  the  flower  of 
the  yucca,  or  Spanish 
bayonet,  a  familiar  plant 
of  the  dry  southwestern 
plains.  During  the  day 
the  female  remains 
quiet,  but  at  dusk  (in 
the  breeding  season)  she 
begins  laying  her  eggs  within  the  pistil  of  the  flowers,  among 
the  ovules,  which,  when  the  flower  is  fertilized,  are  to  grow 
into  seeds.  Upon  these  seeds  the  larva  of  the  Pronuba  will 
feed.  If  this  were  all,  there  would  be  no  peculiarity  deserving 
of  mention;  but  the  female  goes  a  step  farther  and  makes 
sure  of  a  supply  of  seeds  for  the  larva  by  collecting  pollen 
from  the  stamens  and  thrusting  it  into  .the  pistil.  The  ad- 
vantage to  the  larva  is  obvious,  since  its  supply  of  food  is 
rendered  certain ;  the  advantage  to  the  plant  probably  lies  in 
the  fact  that  not  all  the  seeds  thus  provided  for  are  eaten  by 
the  larva  before  reaching  maturity.  This  association  may  be 
cited  as  an  illustration  of  symbiosis. 


FIG.  53.  Pronuba  Moth.  Natural  size. 
(After  Riley) 


THE  INSECTS:    HEXAPODA  93 

Geographical  Distribution  of  Insects.  The  map  on  page  17 
shows  the  region  of  the  United  States  occupied  by  the  Rocky 
Mountain  locust.  Within  a  portion  of  this  area  the  species 
is  able  to  maintain  itself  permanently ;  just  outside  of  this 
area  are  other  regions  which  are  only  temporarily  occupied, 
as  the  great  swarms  forming  periodically  seek  a  new  home. 
That  the  species  is  able  to  maintain  itself  in  one  region  and 
not  in  another  is  due  to  its  adaptation  to  a  particular  region 
in  the  matter  of  food,  temperature,  climate,  absence  of  over- 
powering enemies,  and  other  causes.  Similar  maps  might  be 
drawn  showing  the  geographical  distribution  of  all  the  other 
insects  studied.  In  each  case  there  would  be  found  some 
reason  why  a  particular  insect  did  not  occupy  a  larger  terri- 
tory, since,  generally,  species  tend  by  natural  increase  to 
broaden  their  ranges  till  hindered  by  some  barrier  to  their 
farther  advance.  To  land  animals  such  barrier  may  be  a 
mountain  range,  a  desert,  or  a  large  body  of  water.  To  a 
desert-inhabiting  species  it  might  be  a  forest.  To  aquatic 
animals,  waterfalls  or  rapids  are  often  insurmountable. 
Temperature  conditions  are  very  definite  in  their  effects 
on  the  distribution  of  animal  life.  Food- supply  is  another 
important  factor.  The  ocean  is  a  barrier  to  nearly  all  land 
species. 

The  animal  life  of  any  region  is  known  as  its  fauna.  Though 
insects  are  widely  distributed  over  the  earth,  a  study  of  the 
different  species  shows  that  there  are  more  or  less  well-marked 
areas,  each  of  which  possesses  its  characteristic  species. 
Though  much  overlapping  occurs,  as  might  be  expected  in 
the  case  of  animals  which  can  fly  freely  from  place  to  place, 
yet  on  the  whole  it  is  possible  to  separate  fairly  well-marked 
regions,  the  climatic  and  other  boundaries  of  which  have 
prevented  any  great  intercommunication,  thus  producing 
peculiar  forms  of  life  in  each  region.  These  regions  may  be 
stated  as  follows. 


94  GENERAL  ZOOLOGY 

The  Arctic  realm  includes  all  the  land  in  the  northern 
hemisphere  as  far  south  as  the  northern  limit  of  trees  and 
(so  far  as  the  insects  are  concerned)  the  tops  of  high  moun- 
tains in  the  temperate  zone.  It  has  already  been  noted  that 
the  White  Mountain  butterfly  (p.  48)  belongs  to  this  fauna. 
The  Eurasian  realm  comprises  all  of  Europe  south  of  the 
Arctic  realm ;  Asia,  north  of  the  Himalayas  and  south  of 
the  Arctic  realm ;  and  Africa,  north  of  the  Desert  of  Sahara. 
United  with  this,  by  many  authors,  is  the  North  American 
realm,  embracing  North  America  south  of  the  Arctic  realm 
and  north  of  Mexico.  In  past  time  land  connection  was 
more  complete  than  at  present,  and  considerable  migration 
has  taken  place  from  one  continent  to  the  other.  The  South 
American  realm  comprises  that  portion  of  the  continent  north 
of  Patagonia,  and  includes  the  West  Indies,  Central  America, 
the  greater  part  of  Mexico,  and  a  portion  of  the  most  south- 
erly part  of  Florida.  This  region  has  contributed  many  species 
to  our  own  fauna.  South  of  this  realm  is  another  temperate 
region  in  Patagonia,  which  corresponds  in  position  to  the 
North  American  realm,  but  owing  to  its  comparatively  small 
size  it  is  not  usually  ranked  among  the  great  regions  of  the 
earth.  Its  fauna  is  mainly  derived  from  the  South  American. 
Still  farther  south  is  an  Antarctic  region  of  eternal  snow  and 
ice ;  but  little  is  known  of  the  life  of  this  region,  and  it  may 
be  omitted  from  the  list  of  the  great  faunal  divisions.  The 
African  realm  includes  all  Africa  south  of  the  Desert  of 
Sahara.  With  this  is  often  united  the  Indian  realm,  compris- 
ing the  Asian  continent  south  of  the  Himalayas,  and  the 
East  Indies  as  far  as  the  Strait  of  Lombok.  The  testimony 
of  geology  is  strong  that  these  two  realms  were  once  con- 
nected, though  the  water  is  now  very  deep  and  wide  between 
them.  Madagascar  is  by  some  naturalists  included  within  the 
Indo-African  realm ;  by  others,  considered  a  separate  region. 
The  last  of  the  great  faunal  divisions  is  the  Australian  realm, 


95 

including  Australia,  Papua,  Celebes,  and  Lombok,  and  neigh- 
boring islands  in  the  Pacific  Ocean.  It  seems  to  have  been 
isolated  from  the  other  land  masses  for  a  considerable  period  ; 
it  is  singularly  deficient  in  the  highest  forms  of  life.  Each  of 
the  great  faunal  divisions  is  capable  of  subdivision,  but  into 
the  details  of  this  we  need  not  go. 

Nomenclature  and  Classification  of  Insects.  In  order  to 
write  intelligently  about  animals,  it  is  necessary  that  natural- 
ists should  have  some  uniform  system  of  naming,  or  nomen- 
clature, since  the  common  names  of  animals  vary  not  only  in 
the  different  countries  and  languages  but  even  in  different 
parts  of  the  same  country.  It  will  be  noticed  that  each  insect, 
when  first  spoken  of  in  these  chapters,  is  accompanied  by  a 
scientific  name  printed  in  italics.  Thus  the  Rocky  Mountain 
locust  is  Melanoplus  spretus  ;  the  common  red-legged  locust, 
Melanoplus  femur-rubrum  ;  the  lesser  locust,  Melanoplus  at- 
lanis. These  different  kinds  or  species  of  locust  differ  in  size, 
color,  and  habitat,  and  they  each  receive  a  different  specific 
name,  as  spretus,  femur-rubrum,  and  atlanis.  They  agree  in  other 
characteristics,  such  as  the  general  structure,  size,  and  propor- 
tion of  their  parts,  and  they  are  therefore  placed  in  the  same 
group  or  genus,  —  Melanoplus.  The  word  "  genus  "  is  thus  seen 
to  be  a  term  of  wider  application  than  the  word  "species." 
A  genus  may  include  one  or  several  species.  The  generic  and 
specific  names  make  up  the  complete  scientific  name  of  an 
animal.  The  names  are  always  taken  from  the  Latin  or  Greek, 
or  are  Latinized  in  form,  so  that  they  are  understood  by  all 
scientific  men.  They  often  refer  to  some  striking  character- 
istic of  the  animal  ;  thus,  Melanoplus  means  "  black  armor,"  in 
allusion  to  the  dark-colored  exoskeleton.  Sometimes  the  refer- 
ence is  to  the  locality  where  the  animal  is  found,  as  atlanis, 
referring  to  the  Atlantic  states  ;  sometimes  the  name  is  given 
in  honor  of  some  student  of  animals,  as  Darwin'ii  (see  p.  343), 
named  after  the  naturalist,  Charles  Darwin.  The  scientific 


96  GENERAL  ZOOLOGY 

name  first  given  to  an  animal,  if  accompanied  by  a  descrip- 
tion, is  the  name  it  must  bear,  and  the  species  is  known  under 
that  name  wherever  found.  This  system  of  nomenclature  was 
introduced  by  Linnseus  (see  p.  443). 

We  must  not  overlook  the  fact  that  in  the  study  of  animals 
we  have  to  deal  only  with  individuals.  The  words  "  species," 
"  genus,"  and  the  other  words  used  beyond,  are  man's  inven- 
tion, for  his  convenience  in  scientific  description.  Individuals 
which  resemble  each  other  in  a  large  number  of  characters  — 
and  especially  if  the  individuals  are  able  to  interbreed  —  are 
usually  said  to  belong  to  the  same  species.  The  test  of  inter- 
breeding, while  of  almost  universal  application,  is  not  invari- 
ably a  means  of  distinguishing  the  species,  since  in  some 
cases  two  different  species  can  produce  offspring  (called 
hybrids),  though  the  latter  are  usually  not  fertile,  —  that  is, 
they  are  not  themselves  capable  of  producing  young. 

Often  within  the  limits  of  a  single  species  there  are  groups 
of  individuals  which  vary  from  the  others  in  one  or  more 
characters.  Especially  is  this  true  of  those  species  with  a 
wide  range,  including  different  climatic  conditions.  In  such 
cases  the  different  forms  which  the  species  assumes  are  termed 
varieties,  and  a  varietal  name  is  sometimes  added  to  the 
generic  and  specific  names.  We  have  already  referred  to  the 
seasonal  variations  of  the  black  swallow-tail  butterfly. 

The  different  genera  are  arranged  in  groups,  or  classified, 
according  to  their  resemblances  and  differences.  A  number  of 
genera  which  show  similar  structural  characteristics  of  more 
general  character  than  those  used  to  constitute  a  genus  make 
up  a  family.  Thus  the  locusts,  not  only  of  the  genus  Melano- 
plm  but  also  of  all  the  other  genera  found  in  North  Amer- 
ica, together  with  the  genera  of  the  Old  World,  have  short 
antennae,  in  common  with  other  characteristics,  which  cause 
them  to  be  placed  in  the  locust  family,  Acrid'idce.  Similarly, 
the  katydid  and  other  green  grasshoppers,  with  many  meadow 


THE   INSECTS:    HEXAPODA 


97 


species,  belong  to  the  family  of  long-horn  or  true  grass- 
hoppers, Locust' idee.  The  crickets  (GrryVlidce)  and  the  cock- 
roaches (Blat'tidce)  are  allied  families.  By  common  consent 
family  names  end  in  -idee.  Families  are  united  to  form  orders, 
and  orders  in  turn  make  up  classes.  The  largest  and  most 
important  of  the  orders  which  make 
up  the  class  Hexapoda  have  already 
been  discussed.  As  we  shall  see 
later,  the  classes  are  united  to  form 
phyla  (sing.,  phylum),  the  primary 
divisions  of  the  animal  kingdom. 

Definition  of  Thysanura  (Gr. 
thysanos,  fringe ;  our  a,  tail).  Of 
the  orders  not  mentioned  in  the 
preceding  chapters  it  will  be  neces- 
sary to  refer  only  to  the  Thysanu'ra, 
or  springtails.  The  springtails  are 
small,  flattened,  wingless  insects, 
with  usually  simple  eyes,  and  ap- 
pendages on  some  of  the  abdom- 
inal somites.  They  are  found  under 
stones,  in  damp  places,  or  in  human 
dwellings.  They  develop  from  the 
egg  without  metamorphosis.  The 
best-known  species  is  the  "  silver- 
fish,"  or  "  fish,  moth  "  (Lepis'ma  sac- 
chari'na,  Fig.  54),  often  seen  in  houses,  where  it  sometimes 
does  damage  to  starched  clothing  or  to  the  bindings  of  books. 

Generalized  and  Specialized  Forms.  The  Thysanura  are  espe- 
cially interesting,  since  they  probably  more  closely  resemble 
the  ancestral  type  of  insect  than  do  any  other  living  species. 
The  primitive  or  ancestral  forms  were  probably  naked,  wing- 
less hexapods,  without  strongly  marked  divisions  into  head, 
thorax,  and  abdomen.  Their  legs  were  probably  equal  or 


FIG.  54.  Fishmoth.  Enlarged. 
(After  Marlatt,  Bulletin  No.  4, 
N.S.,  United  States  Depart- 
ment of  Agriculture,  Division 
of  Entomology) 


98  GENERAL  ZOOLOGY 

nearly  equal  in  size.  The  species  probably  developed  from 
the  egg  without  metamorphosis.  The  lack  of  special  adapta- 
tions or  modifications  of  the  various  organs  marks  the  ances- 
tral insects  as  generalized  forms,  as  distinguished  from  their 
more  or  less  specialized  descendants  of  to-day,  in  which  the 
organs  have  become  modified  to  perform  different  functions. 
Thus  the  greatly  developed  hind  legs  of  the  locusts  are  a 
specialization  in  structure,  fitting  the  insect  to  progress  by 
leaps  as  well  as  by  walking. 

Very  different  degrees  of  specialization  often  exist  in  the 
organs  of  the  same  species  ;  thus  the  digestive  system  of 
the  locust  is  quite  complex,  while  the  separate  prothorax  is 
a  generalized  character,  which  shows  the  locust  to  be  allied 
in  this  respect  more  closely  to  the  primitive  type  than  are 
insects  like  the  wasps,  for  example,  where  the  three  divisions 
of  the  thorax  are  grouped  in  one  mass.  Within  the  limits  of 
every  order  there  are  different  degrees  of  specialization,  and 
there  are  cases  in  every  order  where  loss  or  decline  of  parts 
(called  degeneration)  has  been  brought  about  through  various 
causes.  Among  the  May-flies  the  mouth-parts  of  the  imago 
have  become  degenerate  in  connection  with  the  short  adult 
life,  which  lasts  only  long  enough  for  mating  and  the  laying 
of  eggs  for  a  new  generation.  In  some  scale-insects  the  female 
becomes  degenerate  in  connection  with  the  quiescent  life 
beneath  a  protecting  scale.  She  loses  eyes,  antennae,  and  legs, 
becoming  very  little  more  than  a  bag  capable  of  feeding  and 
reproducing.  Parasitism  also  brings  about  degeneration. 

From  the  study  of  the  forms  in  which  different  organs 
appear  in  the  orders  of  insects  (that  is,  from  the  study  of 
morphology,  the  science  of  form)  the  naturalist  is  able  to  say 
which  kinds  of  insects  have,  on  the  whole,  become  most  spe- 
cialized in  structure,  and  those  which  have,  on  the  whole, 
varied  least  from  the  primitive  generalized  type.  The  evi- 
dence from  this  source  points  to  the  fact  that  the  more 


THE  INSECTS:    HEXAPODA  99 

generalized  of  the  orders  which  we  have  mentioned  are  the 
Thysanura,  Plectoptera,  Odonata,  Orthoptera,  and  Hemiptera. 
These  are  the  orders,  it  will  be  remembered,  in  which  meta- 
morphosis is  either  entirely  wanting,  or  where,  if  present, 
there  is  usually  no  well-marked  pupal  resting-stage. 

In  addition  to  morphology,  another  source  of  information 
is  the  geological  record  of  species,  —  the  fossil  remains  of 
organisms  preserved  in  the  mud,  clay,  or  sand  at  the  bottom 
of  water.  Wherever  areas  of  land  are  uplifted,  the  atmos- 
pheric agencies  of  wind  and  water  begin  their  work  of  wear- 
ing them  down  again.  The  worn  materials  in  the  form  of 
clay,  sand,  or  mud,  as  may  be  seen  to-day  after  a  rain,  find 
their  way  in  rivulets  to  lower  ground,  or  into  a  river,  which 
deposits  them  still  lower,  finally  even  to  the  bottom  of  the  sea. 
When  there,  or  in  a  temporary  resting-place  in  some  lake  or 
pond,  the  material  forms  a  bed  into  which  the  remains  of 
animals  may  drop.  Under  favorable  conditions  their  hard 
parts  are  preserved  in  perfect  form,  but  the  substance  in  them 
is  replaced  by  minerals,  and  the  entire  mass  is  consolidated 
into  rock  by  heat  and  the  pressure  of  other  materials  upon  it. 
Footprints  may  also  be  made  in  the  soft  mud  at  the  edge  of 
ponds,  and  indelibly  preserved  in  the  rocks  of  later  times. 

The  geologist  has  worked  out  in  detail  the  order  in  which 
the  rock  material  of  the  world  has  been  laid  down.  By  study- 
ing the  fossil  remains  of  living  things  the  zoologist  can 
picture  something  of  the  life  of  each  of  the  great  epochs  in  the 
earth's  history,  thpugh  owing  to  the  conditions  of  preserva- 
tion, by  far  the  greater  part  of  the  record  has  been  lost.  It  is 
as  though  we  should  try  to  get  a  connected  idea  of  the  history 
of  the  United  States  from  a  book  from  which  had  been  torn 
the  whole  of  the  early  voyages,  much  of  the  colonial  period, 
and  many  pages  from  the  story  of  the  Revolution,  the  Civil 
War,  and  later  history.  Unfortunately  the  geological  record 
is  especially  incomplete  with  regard  to  the  insects,  so  that  it 


100  GENERAL  ZOOLOGY 

does  not  give  us  much  help  in  this  particular  problem.  How- 
ever, of  the  remains  of  winged  insects  which  have  so  far  been 
discovered,  the  earliest  are  those  belonging  to  the  orders 
Orthoptera,  Hemiptera,  Plectoptera,  and  Odonata. 

A  third  source  of  information  comes  from  the  study  of  the 
earlier,  or  embryological,  stages  in  the  development  of  the 
individual.  According  to  von  Baer,  a  Russo-German  natural- 
ist born  in  1792,  the  more  nearly  alike  two  animals  belonging 
to  the  same  phylum  are,  the  greater  will  be  the  resemblance 
in  their  embryological  stages ;  that  is,  the  longer  will  the 
animals  continue  to  follow  a  similar  line  of  development. 
This  is  known  as  von  Baer's  law.  Since  his  time  the  theory 
has  been  advanced  that  each  individual  animal,  being  the 
product  of  its  ancestors,  reproduces  to  a  greater  or  less  extent 
the  stages  which  have  occurred  in  the  history  of  the  race. 
According  to  this  view  the  earlier  stages  in  the  history  of 
the  individual  represent  adult  stages  in  the  life  of  the  past. 
This  is  known  as  the  recapitulation  theory.  This  principle 
applied  to  the  cockroaches  (see  p.  20),  would  indicate  their 
descent  from  ancestors  which  were  more  cylindrical  than  the 
flattened  forms  of  to-day. 

The  conclusions  of  embryology  justify  the  general  state- 
ments just  made,  so  that  it  is  possible  to  assert  that  the  orders 
without  strongly  marked  metamorphosis  are,  on  the  whole,  the 
"  lower,"  or  more  generalized,  insects ;  while  the  orders  with 
marked  ("  complete")  metamorphosis  represent  the  "highest," 
or  most  specialized,  types  of  the  class  to-day.  The  sequence 
in  which  the  different  orders  of  insects  have  been  described 
in  these  pages  represents,  on  the  whole,  with  the  excep- 
tion of  the  Thysanura,  a  gradually  ascending  series  from  the 
more  generalized  forms  to  the  highly  specialized  Lepidoptera, 
Diptera,  and  Hymenoptera. 


CHAPTER  X 
THE  DOCTRINE  OF  EVOLUTION 

To  the  open  ear  it  sings 

Sweet  the  genesis  of  things, 

Of  tendency  through  countless  ages, 

Of  star-dust  and  star  pilgrimages, 

Of  rounded  worlds,  of  space  and  time, 

Of  the  old  flood's  subsiding  slime, 

Of  chemic  matter,  force  and  form, 

Of  poles  and  powers,  cold,  wet,  and  warm. 

EMERSOX,  Wood  Notes. 

Definition  of  Evolution.  The  word  "  evolution,"  in  its  most 
general  sense,  signifies  a  process  of  unfolding  or  develop- 
ment, and  it  is  in  this  sense  that  we  speak  of  the  evolution 
of  a  plan  or  the  evolution  of  history.  In  science,  generally, 
the  word  is  used  to  express  the  process  of  development  from 
simplicity  to  complexity ;  that  is,  in  the  words  of  the  Century 
Dictionary,  "  to  a  nicer  and  more  elaborate  means  for  reach- 
ing definite  ends,  the  process  being  regarded  as  of  the  nature 
of  a  growth."  In  this  sense  we  speak  of  the  evolution  of  our 
solar  system  from  a  mass  of  heated  gaseous  material  (see 
p.  293).  In  biology  (the  science  which  has  to  do  with  living 
things,  —  both  plants  and  animals)  the  word  is  used  not  only 
to  signify  the  development  of  an  individual  organism  from 
the  egg  to  maturity,  but  it  serves  to  characterize  a  particular 
view  as  to  the  derivation  of  all  organisms  by  natural  descent, 
with  modification  of  earlier  and  simpler  forms  of  life.  Biolo- 
gists are  generally  agreed  that  all  the  many  species  of  animals 
and  plants  of  to-day  have  come  to  their  present  form  through 
evolution,  though  the  steps  by  which  this  evolution  has  been 
accomplished  are  not  thoroughly  understood.  A  classification 

101 


102  GENE.RAL  ZOOLOGY 

of  animals  is  not  a  mere  grouping  of  species  which  resemble 
each  other  to  a  greater  or  less  extent,  but  is  rather  an  attempt 
at  a  statement  of  the  truth  of  evolution,  aiming  to  express 
the  relationships  existing  between  animals,  as  shown  not  only 
in  their  present  structure  but  also  by  their  development  from 
egg  to  maturity,  and  their  history  through  geological  time. 

While  every  species  of  animal  tends  to  produce  young 
resembling  itself,  no  two  individuals  of  any  species  are  ever 
precisely  alike.  That  the  young  of  each  species  tend  to 
resemble  their  parents,  we  say  is  due  to  heredity  ;  that  they 
never  exactly  resemble  them,  we  say  is  due  to  variation.  Of 
the  causes  underlying  heredity  and  variation  we  know  almost 
nothing.  We  notice  that  in  the  course  of  time  various  forms 
of  life  have  appeared  on  the  earth,  and  that  on  the  whole 
there  has  been  a  gradually  increasing  complexity  in  animal 
structure  through  geological  time,  the  more  complex  animals 
following  the  simpler,  as  the  environment  has  changed  and 
new  conditions  have  arisen.  Because  of  the  incompleteness 
of  the  knowledge  of  the  evolution  of  life  on  the  earth,  we 
can  do  little  more  than  call  attention  to  some  of  the  second- 
ary factors  in  evolution,  without  attempting  to  measure,  ex- 
cept in  a  rough  way,  their  relative  importance. 

Natural  Selection.  With  the  principle  of  natural  selection 
are  associated  the  names  of  Charles  Darwin  and  Alfred  Russel 
Wallace,  who  independently  stated  it  in  papers  published  in 
1858  (see  p.  450).  The  principle  had  been  recognized  before, 
but  as  stated  by  Darwin  it  was  reenforced  by  such  a  wealth 
of  illustration  that  it  compelled  the  attention  of  the  scien- 
tific world. 

In  introducing  the  discussion  of  natural  selection,  Darwin 
makes  use  of  the  principle  of  artificial  selection  among  domes- 
ticated animals,  —  that  is,  the  selection  by  man  of  certain 
individuals  having  peculiarities  which  he  wishes  to  preserve. 
These  individuals  are  allowed  to  breed  together,  and,  in  the 


THE  DOCTRINE  OF  EVOLUTION  103 

next  generation,  those  individuals  varying  in  the  direction 
desired  are  again  chosen  for  breeding.  If  the  process  is  con- 
tinued through  several  generations  it  may  produce  a  race  in 
which  the  special  characteristic  desired  is  fixed.  Artificial 
selection  is  one  of  the  means  by  which  the  different  races  of 
domesticated  animals  and  plants  have  been  produced. 

According  to  Darwin,  something  similar  to  this  artificial 
selection  by  man  goes  on  in  nature,  producing  the  different 
species  of  animals  as  we  know  them  to-day.  All  organisms 
tend  to  vary.  Some  variations,  he  says,  are  due  to  changes  in 
the  conditions  of  life  and  to  excess  of  food  (these  two  under- 
lying the  great  variability  of  domesticated  animals) ;  others 
are  due  to  the  nature  of  the  organism ;  to  the  inherited 
effect  of  habit  and  the  use  and  disuse  of  parts ;  or  to  rever- 
sion to  characters  once  possessed  by  ancestors.  The  varia- 
tions.which  occur  are  of  two  kinds,  —  definite  and  indefinite. 
Indefinite,  or  fluctuating,  variations  are  those  comparatively 
slight  differences  which  occur  constantly  among  animals  and 
plants,  so  that  of  all  the  individuals  of  the  same  species, 
no  two  are  ever  exactly  alike.  Definite  variations  are  more 
striking ;  of  these  the  an  con  ram  is  an  example.  This  ani- 
mal, born  in  Massachusetts  in  1791,  of  an  ordinary  breed  of 
sheep,  had  a  long  back  and  short,  crooked  legs.  From  it, 
by  crossing,  has  been  produced  the  ancon  breed  of  sheep, 
showing  the  same  peculiarities  as  its  progenitor.  The  breed 
was  highly  prized  for  a  time  on  account  of  the  inability  of 
the  animals  to  jump  fences.  Darwin  lays  most  stress  upon 
the  fluctuating  variation  as  affording  the  material  for  natural 
selection.  * 

In  order  to  understand  the  principle  of  natural  selection,  we 
must  consider  for  a  moment  the  struggle  for  existence.  This 
term  is  used  by  Darwin  in  "  a  large  and  metaphorical  sense, 
including  dependence  of  one  being  on  another,  and  including 
(which  is  more  important)  not  only  the  life  of  the  individual 


104 


GENERAL  ZOOLOGY 


but  also  success  in  leaving  progeny."  The  struggle  results 
from  the  tendency  of  living  things  to  increase  more  rapidly 
than  the  means  of  subsistence.  Professor 
Jordan,  of  Leland  Stanford  Junior  Uni- 
versity, says,  "  If  the  eggs  of  a  common 
house-fly  should  develop,  and  each  of  its 
progeny  should  find  the  food  and  tempera- 
ture it  needed,  with  no  loss  and  no  des- 
truction, the  people  of  a  city  in  which  this 
might  happen  could  not  get  away  soon 
enough  to  escape  suffocation  from  a  plague 
of  flies."  Professor  Thomson,  of  Edinburgh, 
Scotland,  gives  this  illustration:  "A  female 
aphis,  often  producing  one  offspring  per 
hour  for  days  together,  might  in  a  season 
be  the  ancestor  of  a  progeny  of  atomies 
which  would  weigh  down  five  hundred 


FIG.  55.  Caddice-Flies.    Enlarged 


THE  DOCTRINE  OF  EVOLUTION  105 

millions  of  stout  men."  A  similar  rapid  increase  would  be 
noted  on  the  part  of  any  animal,  were  the  various  checks  to 
its  multiplication  removed.  The  struggle  for  life  goes  on 
between  different  individuals  of  the  same  species,  as  in  a 
swarai  of  locusts ;  between  individuals  of  different  species, 
as  with  locusts  and  insect-eating  birds,  and  with  the  con- 
ditions of  existence,  such  as  temperature,  winds,  moisture, 
and  food-supply. 

Owing  to  the  struggle  for  existence,  Darwin  says:  "Varia- 
tions, however  slight,  and  from  whatever  cause  proceeding, 
if  they  be  in  any  degree  profitable  to  the  individuals  of  a 
species,  in  their  infinitely  complex  relations  to  other  organic 
beings  and  to  their  physical  conditions  of  life,  will  tend  to 
the  preservation  of  such  individuals,  and  will  generally  be 
inherited  by  the  offspring.  The  offspring,  also,  will  have  a 
better  chance  of  surviving,  for,  of  the  many  individuals  of 
any  species  which  are  periodically  born,  but  a  small  number 
can  survive." 

The  caddice-flies  are,  in  their  immature  stage,  aquatic 
larvae  which  build  protective  cases  composed  of  grains  of 
sand,  or  bits  of  straw,  or  leaves  (Fig.  55).  These  cases  afford 
concealment  and  protection  to  the  young.  Applying  the  prin- 
ciple of  natural  selection  here,  it  would  be  said  that  those 
caddice-flies  which  varied  in  the  direction  of  protective  cases 
have  survived,  and  those  which  did  not  have  been  devoured 
or  otherwise  destroyed ;  hence  a  race  of  case-building  cad- 
dice  flies  is  in  existence  to-day.  Natural  selection  results  in 
"the  survival  of  the  fittest"  for  the  environment,  and  the 
principle  is  used  to  explain  the  degeneration  due  to  parasi- 
tism, as  well  as  the  development  of  increased  complexity  in 
animal  structure. 

We  have  spoken  of  the  conflict  between  individuals  of  the 
same  species  for  the  necessities  of  existence,  but  many  species, 
individually  rather  weak,  become  successful  competitors  in 


106  GENERAL  ZOOLOGY 

the  struggle  for  existence  by  mutual  aid  and  cooperation. 
Prince  Kropotkin  has  recently  called  attention  to  cases  of 
mutual  aid  in  the  animal  kingdom.  He  says :  "  As  soon  as 
we  study  animals  —  not  in  laboratories  and  museums  only, 
but  in  the  forest  and  the  prairie,  in  the  steppe  and  the  moun- 
tain —  we  at  once  perceive  that  though  there  is  an  immense 
amount  of  warfare  and  extermination  going  on  amidst  vari- 
ous species,  and  especially  amidst  various  classes  of  animals, 
there  is,  at  the  same  time,  as  much,  or  perhaps  even  more,  of 
mutual  support,  mutual  aid,  and  mutual  defense  amidst  ani- 
mals belonging  to  the  same  society.  Sociability  is  as  much  a 
law  of  nature  as  mutual  struggle."  Illustrations  may  be  seen 
in  the  complicated  communities  of  the  ants,Jbees,  and  wasps 
among  the  insects ;  others  occur  among  the  birds  and  fur- 
bearing  animals  (see  Chapters  XXIX  and  XXXI). 

Sexual  Selection.  The  principle  of  sexual  selection,  also 
formulated  by  Darwin,  is  an  extension  of  the  principle  of 
selection  to  account  for  the  secondary  sexual  characters  which 
exist  in  many  animals.  In  most  insects,  where  there  is  sexual 
dimorphism,  the  male,  though  usually  smaller,  is  more  brightly 
colored ;  it  is  armed  or  ornamented  with  spines,  which  the 
female  does  not  possess,  or  it  has  special  sound-producing 
'organs.  In  the  common  stag-beetle  (Luca'nus,  Fig.  56)  the 
mandibles  of  the  male  are  of  larger  size  than  those  of  the 
female.  Among  the  birds,  in  those  cases  where  the  sexes  are 
differently  colored,  the  males  are  usually  more  brilliant ;  they 
often  have  spurs,  wattles,  crests,  or  plumes,  while  the  females 
are  without  these  structures,  or  have  them  in  less  degree. 
It  is  only  the  male  birds,  too,  which  possess  the  gift  of  song. 
Among  the  fur-bearers  special  characteristics,  such  as  horns, 
antlers,  and  tusks,  often  occur.  These  various  secondary 
sexual  differences  are  ascribed  by  Darwin  to  sexual  selection, 
which  "depends,  not  on  a  struggle  for  existence  in  relation 
to  other  organic  beings  or  to  external  conditions,  but  on  a 


THE  DOCTRINE  OF  EVOLUTION  107 

struggle  between  the  individuals  of  one  sex,  generally  the 
males,  for  the  possession  of  the  other  sex.  The  result  is  not 
death  to  the  unsuccessful  competitor,  but  few  or  no  offspring. 
Sexual  selection  is,  therefore,  less  rigorous  than  natural  selec- 
tion. Generally  the  most  vigorous  males,  those  which  are  best 
fitted  for  their  place  in  nature,  will  leave  most  progeny.  But 
in  many  cases  victory  depends  not  so  much  on  general  vigor 


FIG.  56.   Stag-Beetle  (male  and  female).    Natural  size 


as  on  having  special  weapons  confined  to  the  male  sex.  A 
hornless  stag  or  spurless  cock  would  have  a  poor  chance 
of  leaving  numerous  offspring."  The  greater  brilliancy  of 
many  males  is  accounted  for  by  ascribing  it  to  the  choice 
by  the  females,  through  countless  generations,  of  the  most 
brilliantly  colored  and  attractive  males.  The  song  of  male 
birds  is  accounted  for  in  a  similar  manner. 

The  Inheritance  of  Acquired  Characters.  Though  Darwin 
considered  that  species  have  arisen  largely  through  the  action 
of  natural  selection  on  favorable  variations,  he  admitted  also 
other  factors  in  evolution,  on  which  some  naturalists  to-day 
lay  great  stress.  It  is  a  truism  of  our  everyday  life  that  the 
use  of  an  organ  sooner  or  later  affects  its  structure.  Thus 
the  brawny  arm  of  the  blacksmith  may  be  directly  attributed 
to  the  kind  of  work  he  does.  There  are  many  cases  in  the 
animal  kingdom  where  the  characters  of  animals  might  be 
interpreted  as  due  to  the  use  or  disuse  of  organs.  Among 
the  insects  we  may  instance  the  enlarged  fore  legs  of  the 


108  GENERAL  ZOOLOGY 

mole-cricket  and  mantids,  the  enlarged  hind  legs  of  the  locust, 
and  the  absence  of  eyes  in  certain  cave-inhabiting  insects. 
With  this  principle  are  associated  the  names  of  Erasmus 
Darwin,  grandfather  of  Charles  Darwin,  and  the  French 
naturalist  Lamarck  (see  p.  448). 

The  chief  difficulty  in  the  application  of  the  principle  of  the 
inheritance  of  acquired  characters  as  a  factor  in  evolution  lies 
in  the  fact  that  we  have  little  or  no  evidence  that  the  charac- 
ters acquired  by  use  or  disuse  during  the  life  of  an  individual 
are  transmitted  to  its  descendants,  though  some  effort  has 
been  made  of  late  years  to  furnish  this  direct  evidence.  The 
most  important  experiments  along  this  line  are  those  of  Brown- 
Sequard,  a  Franco- American  physiologist  (1819—1894).  Pie 
succeeded  in  producing  epilepsy  in  guinea-pigs  born  of  parents 
which  had  been  rendered  epileptic  by  an  injury  to  the  spinal 
cord.  Exophthalmia  (a  disease  characterized  by  abnormal 
protrusion  of  the  eyeball)  was  also  transmitted  through  sev- 
eral generations.  Certain  mutilations,  produced  by  the  ani- 
mals eating  off  their  hind-leg  toes  after  the  latter  have  been 
rendered  insensible  to  pain  by  cutting  the  nerve  leading  to 
them,  also  seem  in  some  cases  to  have  been  transmitted  to  the 
descendants.  The  objection  is  made  to  these  experiments 
that  they  may  show  the  result  of  a  transmitted  disease  rather 
than  the  inheritance  of  an  acquired  character. 

The  Direct  Influence  of  the  Environment.  In  connection 
with  the  principle  of  the  inheritance  of  characters  acquired 
through  use  or  disuse,  Lamarck  held  that  the  changes  in  the 
environment  directly  brought  about  changes  in  the  organism, 
and  that  these  changes  were  transmitted,  to  the  descendants 
(see  p.  449).  This  and  the  preceding  principle  are  therefore 
often  spoken  of  as  Lamarckian  factors  in  evolution,  while 
natural  and  sexual  selection  are  termed  Darwinian  factors. 

All  organisms  have  to  exist  under  certain  conditions  of 
pressure  either  of  liquids  or  gases;  they  are  adapted  to  a 


THE  DOCTRINE  OF  EVOLUTION  109 

certain  range  of  temperature,  moisture,  and  light ;  they  require 
more  or  less  oxygen ;  and  they  need  a  certain  amount  and 
quality  of  food.  As  a  general  rule  slight  changes  in  these 
various  elements  of  the  environment  can  be  borne  without 
injury;  greater  changes  may  cause  death.  There  are  a  num- 
ber of  cases  in  the  animal  kingdom  where  modifications  in 
the  organism  seem  to  be  directly  connected  with  environ- 
mental changes,  though  it  is  not  always  easy  to  say  what  fac- 
tor in  the  environment  is  responsible  for  the  change.  Thus  it 
has  been  stated  that  horses  tend  to  decrease  in  size  in  north- 
ern latitudes,  on  islands,  and  on  mountains.  Most  of  the 
animals  on  islands  are  smaller  than  their  continental  relatives. 
De  Varigny,  in  his  Experimental  Evolution,  says  that,  "  In 
the  Canary  Islands  the  oxen  of  one  of  the  smaller  islands  are 
much  smaller  than  those  of  the  others,  although  all  belong  to 
the  same  breed;  and  the  horses  are  also  smaller,  and  the 
indigenous  inhabitants  are  in  the  same  case,  although  belong- 
ing to  a  tall  race."  The  same  author  also  cites  the  experi- 
ments of  Karl  Semper,  who  stated  that  if  the  common 
pond-snail  of  Europe  is  kept  in  small  volumes  of  water,  — 
less  than  five  or  six  liters  (a  little  over  four  or  five  quarts),  — 
the  animals  do  not  attain  their  usual  size,  but  remain  more 
or  less  dwarfed.  The  differences  between  the  geographical 
varieties  of  the  gray  squirrel  are  given  on  page  406.  Among 
the  insects  the  influence  of  food  in  the  production  of  the 
queen  bee,  and  the  influence  of  temperature  in  the  produc- 
tion of  the  different  broods  of  one  of  the  swallow-tail  butter- 
flies have  already  been  commented  upon.  It  has  also  been 
found  that  colored  bodies  in  the  vicinity  affect  the  colors  of 
the  pupae  of  certain  butterflies  (Fig.  57).  Such  color  changes 
are  due  to  the  susceptibility  of  the  larva  to  surrounding  colors 
during  a  quiescent  period  before  pupation.  The  experiments 
on  Arte'mia,  described  on  page  148,  may  also  be.  referred  to  in 
this  connection. 


110 


GENERAL  ZOOLOGY 


The  difficulty  in  adopting  this  principle  as  an  explanation 
of  the  way  in  which  evolution  has  taken  place  lies  in  the  fact 

already  mentioned  in 
the  discussion  of 
characters  acquired 
through  use  or  dis- 
use, —  that  it  is  not 
yet  entirely  clear  that 
changes  occurring 
during  the  lifetime 
of  the  individual  are 
transmitted  to  the 
next  generation. 

The  Mutation 
Theory.  It  will  be  re- 
membered that  Dar- 
win laid  stress  upon 
indefinite,  or  fluctu- 
ating, variations  as 
furnishing  the  greater 
part  of  the  material 
for  selection.  The  mu- 
FIG.  57.  Pupse  of  Black  Swallow-l^ai!  Butterfly  tation  theorv  stands 

Showing  influence  of  color  of  near-by  object  on  the    in  sharp  Contrast  with 
color  of  the  pupa.  Photographed  from  life.  About    .-,  -,       ,-  ,, 

three  quarters  natural  size  the     Selection    theory 

(From  Hunter's  Studies  in  Insect  Life)  in     emphasizing     the 

heredity  transmission 

of  definite  variations.  With  the  mutation  theory  is  particularly 
associated  the  name  of  Hugo  de  Vries,  a  Dutch  botanist  living 
in  Amsterdam,  Holland.  He  was  led  to  express  the  princi- 
ple from  his  studies  of  the  variations  of  a  species  of  even- 
ing primrose  introduced  from  America  and  found  growing  in 
waste  places  in  Hilversum,  near  Amsterdam.  It  should  not 
be  overlooked  that  William  Bateson,  of  Cambridge,  England 


THE  DOCTRINE  OF  EVOLUTION  111 

(born  1861),  emphasized  the  evolutionary  importance  of  dis- 
continuous variations  (mutations)  years  before  de  Vries'  work 
appeared.  One  of  the  most  recent  general  statements  of  the 
principle  is  to  be  found  in  Evolution  and  Adaptation,  by 
Professor  Thomas  Hunt  Morgan  of  Columbia  University. 
From  his  book  most  of  the  following  statements  have  been 
taken. 

According  to  this  principle  new  species  have  been  pro- 
duced by  sudden  and  perfectly  definite  changes  (mutations) 
in  the  organism,  though  it  is  not  necessary  to  assume  that 
these  changes  are  always  great.  The  theory  makes  no  attempt 
to  account  for  the  presence  of  mutations,  but  when  they 
occur  it  is  a  striking  fact  that  the  characters  tend  to  be 
transmitted  to  the  descendants.  De  Vries  is  inclined  to  think 
that  there  are  periods  of  mutation  when  many  and  great 
changes  take  place,  and  periods  where  comparatively  little 
change  in  the  organism  occurs.  The  same  mutation  may 
occur  time  after  time  and  in  large  numbers  of  individuals. 
When  a  mutation  appears  its  survival  will  depend  on  whether 
it  can  find  a  place  in  nature  where  it  can  exist  and  leave 
descendants.  If  the  organism  is  well  adapted  to  its  environ- 
ment, it  will  leave  many  descendants ;  if  it  is  poorly  adapted, 
it  may  barely  succeed  in  existing.  Useless  or  even  slightly 
injurious  characters  may  appear,  and  if  they  do  not  too  seri- 
ously affect  the  perpetuation  of  the  race,  they  may  persist. 
Since  the  mutations  appear  fully  formed,  there  is  no  diffi- 
culty in  accounting  for  the  early  stages  of  an  organ.  Thus, 
on  the  supposition  of  natural  selection,  it  is  difficult  to  see, 
for  example,  how  the  first  slight  movement  of  the  eye  of  the 
flounder  toward  the  upper  side  (see  p.  320)  could  be  a  favor- 
able variation,  which  it  should  be  according  to  the  selection 
theory,  in  order  to  be  preserved.  Again,  a  difficulty  in  the 
selection  theory  lies  in  the  fact  that  the  differences  between 
allied  species  consist  largely  in  differences  of  unimportant 


112  GENERAL  ZOOLOGY 

organs,  but  this  is  the  condition  we  should  expect,  according 
to  the  mutation  theory. 

Professor  Morgan  brings  his  discussion  to  a  close  by  a 
statement  contrasting  the  mutation  theory  with  the  selec- 
tion theory,  as  follows :  "Animals  and  plants  are  not  changed 
in  this  or  in  that  part  in  order  to  become  better  adjusted 
to  a  given  environment,  as  the  Darwinian  theory  postulates. 
Species  exist  that  are  in  some  ways  very  poorly  adapted  to 
the  environment  in  which  they  must  live.  If  competition 
were  as  severe  as  the  selection  theory  assumes,  this  imper- 
fection would  not  exist. 

"  In  other  cases  a  structure  may  be  more  perfect  than  the 
requirements  of  selection  demand.  We  must  admit,  therefore, 
that  we  cannot  measure  the  organic  world  by  the  measure  of 
utility  alone.  If  it  be  granted  that  selection  is  not  a  mold- 
ing force  in  the  organic  world,  we  can  more  easily  understand 
how  both  less  perfection  and  greater  perfection  may  be  present 
than  the  demands  of  survival  require. 

"  If  we  suppose  that  new  mutations  and  4  definitely  '  inher- 
ited variations  suddenly  appear,  some  of  which  will  find  an 
environment  to  which  they  are  more  or  less  well  fitted,  we 
can  see  ho^w  evolution  may  have  gone  on  without  assuming 
new  species  have  been  formed  through  a  process  of  competi- 
tion. Nature's  supreme  test  is  survival.  She  makes  new 
forms  to  bring  them  to  this  test  through  mutation,  and  does 
not  remodel  old  forms  through  a  process  of  individual 
selection." 

MendePs  Law  of  Heredity.  Considerable  attention  has 
lately  been  given  to  the  experimental  study  of  heredity  and 
variation  by  breeding  animals  and  plants  under  close  observa- 
tion. Among  the  animals  thus  observed  have  been  mice, 
guinea-pigs,  and  rabbits.  Little  has  been  done  along  this 
line  with  the  insects.  These  experiments  have  been  of  great 
interest  in  connection  with  what  is  known  as  Mendel's  law. 


THE  DOCTRINE  OF  EVOLUTION  113 

Gregor  Mendel  was  an  Austrian  monk,  who  experimented 
with  plants  in  his  garden,  and  in  1865  communicated  to  the 
Society  of  Naturalists  at  Briinn  the  substance  of  what  has 
since  been  described  as  "  the  greatest  discovery  in  biology 
since  Darwin."  As  the  result  of  later  experiments  the  law 
was  rediscovered  by  Bateson.  In  our  own  country  Professor 
Castle,  of  Harvard  University,  has  made  observations  on  many 
successive  generations  of  guinea-pigs,  mice,  and  rabbits.  The 
substance  of  most  of  the  following  statements  has  been  taken 
from  his  studies. 

Mendel's  law  asserts  that  when  mating  occurs  between  two 
animals  differing  in  some  character,  the  offspring  (hybrids) 
will  frequently  exhibit  the  characters  of  one  parent  only. 
A  particular  character  exhibited  in  that  way  is  said  to  be 
"  dominant."  If  albino  rabbits  (white,  with  pink  eyes)  are 
crossed  with  gray  rabbits,  all  the  offspring  are  gray,  that  color 
being  dominant.  The  character  (in  this  case,  whiteness)  which 
is  not  seen  in  the  immediate  offspring  is  said  to  be  "recessive." 
That  the  albinism  (white  character)  is  really  present  in  the 
second  generation,  although  invisible,  may  be  demonstrated 
by  permitting  pairs  of  these  hybrid  rabbits  to  breed.  The 
principle  may  be  called  "  the  law  of  dominance."  It  does  not 
seem  to  be  of  universal  application,  as  sometimes  the  young 
have  a  character  of  their  own.  Thus,  if  a  lop-eared  rabbit  is 
bred  with  a  short-eared  rabbit,  the  young  will  have  ears  of 
an  intermediate  length.  There  is  no  way  of  knowing  what 
the  character  of  the  young  will  be  ;  it  can  only  be  determined 
by  experiment.  When  once  determined,  however,  the  char- 
acter is  always  the  same  for  every  hybrid,  provided  the  par- 
ents are  of  pure  breeds. 

The  essential  part  of  Mendel's  discovery  is  this :  that 
the  hybrids  resulting  from  the  crossing  of  animals,  such  as 
white  and  gray  rabbits  already  spoken  of,  whatever  their  own 
character,  will  produce  ripe  germ-cells  (reproductive  cells, 

a  o 


114  GENERAL  ZOOLOGY 

see  p.  210),  which  bear  only  the  pure  character  of  one 
parent  or  the  other,  but  never  both ;  and  these  will  be  pro- 
duced in  equal  numbers.  This  is  known  as  "  the  law  of  the 
purity  of  the  germ-cells."  From  this  law  follows  the  occur- 
rence in  the  next  and  succeeding  hybrid  generations  of  a 
definite  number  of  forms  in  definite  numerical  proportions. 
Thus  in  the  third  generation  of  rabbits,  produced  by  the 
breeding  together  of  the  progeny  of  the  gray  and  the  albino 
rabbits  already  referred  to,  there  are,  in  nearly  every  case, 
three  gray  young  to  one  albino.  Results  similar  to  these 
were  obtained  by  Professor  Castle  with  mice  and  guinea- 
pigs  also. 

The  explanation  of  why  a  character  may  manifest  itself  in 
the  third  generation,  after  being  invisible  in  the  second,  is 
to  be  found  in  the  theory  that  characters  of  organisms  are 
transmitted  from  generation  to  generation  only  in  the  germ- 
cells,  and  by  extremely  minute  bodies,  called  chromosomes, 
within  these  cells.  The  second  generation  is  all  gray,  because 
in  the  united  germ-cells  from  male  and  female  parents  the 
chromosomes  which  bear  the  gray  character  are  more  powerful 
to  express  themselves  in  the  appearance  of  the  young  which 
is  produced  than  are  those  chromosomes  which  bear  the 
albino  character.  However,  the  albino  chromosomes  are  not 
destroyed,  but  are  carried  along  with  the  others  and  give 
rise  to  other  chromosomes  of  their  own  kind,  until,  in  the 
experiment  of  breeding  two  hybrids,  there  occurs  the  oppor- 
tunity for  one  albino  germ-cell  from  each  of  the  two  sexes 
to  unite  and  produce  an  albino  young.  The  mathematical 
chances  of  such  an  occurrence  may  be  expressed  in  an  alge- 
braic formula  in  which  D  represents  dominant  germ-cells 
(half  the  total  number)  and  R  represents  recessive  germ- 
cells  (half  the  total  number).  A  D-cell  may  unite  with 
another  Z>-cell,  or  it  may  unite  with  an  It-cell.  Similarly  an 
R-cell  may  unite  with  an  A'-cell  or  with  a  D-cell,  thus : 


THE   DOCTRINE   OF  EVOLUTION  115 

D         and         R 


Of  the  three  dominant  individuals  one  is  a  pure  dominant, 
but  it  is  impossible  to  say  at  first  which  one  that  is,  except 
by  further  breeding.  The  pure  dominant,  when  bred  with 
another  pure  dominant,  will  produce  only  gray  rabbits,  and 
these  will  produce  gray  rabbits  generation  after  generation. 
Albinos  ^obtained  in  experiments  like  the  one  described  will 
breed  true  generation  after  generation,  if  mated  with  other 
albinos.  When  one  of  the  hybrid  dominants,  D(R),  is  mated 
with  a  recessive  animal,  half  the  young  are  hybrid  dominants 
and  half  are  recessives.  Two  hybrid^  mated  will  produce 
young  in  the  proportion  of  three  gray  to  one  albino,  as  in  the 
third  generation. 

Experiments  to  determine  the  dominant  or  recessive  nature 
of  other  characters,  such  as  length  of  hair  and  smoothness  of 
coat,  show  that  short  hair  in  guinea-pigs  dominates  over  long 
hair,  and  a  rough  coat  over  a  smooth  coat.  It  is  also  true 
that  the  various  characters,  so  far  as  tested,  are  inherited 
quite  independently  of  one  another.  A  smooth  coat  may  be 
associated  with  white  hair  or  with  pigmented  hair  in  guinea- 
pigs,  and  a  rough  coat  also  with  white  hair  or  with  pigmented 
hair.  An  experimenter,  by  controlling  the  combinations  of  a 
number  of  characters,  knowing  which  is  dominant  and  which 
recessive,  may  produce  several  distinct  types  of  animals 
within  the  same  species. 

If  future  experiments  should  support  Mendel's  law,  we 
should  then  be  able  to  understand  how  it  is  that  races  sud- 
denly spring  into  existence  in  nature  and  become  established. 


CHAPTER  XI 

THE  SPIDERS   AND  ALLIES  (ARACHNIDA)    AND  THE  CENTI- 
PEDS  AND  MILLEPEDS  (MYRIAPODA) 

A  noiseless,  patient  spider, 

I  marked  where,  on  a  little  promontory,  it  stood  isolated  ; 
Marked  how,  to  explore  the  vacant,  vast  surrounding, 
It  launched  forth  filament,  filament,  filament  out  of  itself  ; 
Ever  unreaching  them  —  ever  tirelessly  speeding  them. 

WALT  WHITMAN. 

Spiders.  Spiders  have  several  of  the  anterior  somites  joined 
into  a  single  mass,  the  head-thorax,  or  cephalothorax(Fig.5S,  1), 
followed  by  the  nearly  spherical  abdomen  (Fig.  58,  2).  The 
cephalothorax  bears  six  pairs  of  appendages,  —  two  pairs 
of  the  nature  of  jaws  and  four  pairs  of  walking-legs  (Fig. 
58,  3).  The  mandibles  (Fig.  58,  4),  the  first  pair  of  jaws,  are 
appendages  composed  of  two  segments,  of  which  the  terminal 
segment  is  sharp-pointed  and  hollow,  for  the  passage  of  a 
poisonous  secretion  from  a  gland  placed  partly  in  the  head 
and  partly  in  the  basal  segment.  The  second  pair  of  jaws,  or 
maxillce,  bear  jointed  palpi  (Fig.  58,  5),  used  for  handling  food. 
On  the  front  of  the  head  are  eight  simple  eyes ;  compound 
eyes  and  an  ten  use  are  wanting. 

Two  little  slits  on  the  under  side  of  the  abdomen  open 
into  the  breathing-organs  (Fig.  58,  6),  which  consist  of  a  pair 
of  sacs  containing  a  number  of  thin  plates,  like  the  leaves  of 
a  book,  through  which  the  blood  passes  for  the  exchange 
of  gases.  Between  the  two  slits  are  the  external  openings 
of  the  reproductive  organs  (Fig.  58,  7).  At  the  end  of  the 
body  are  three  pairs  of  spinnerets  (Fig.  58,  0),  consisting  of 
a  number  of  little  tubes  leading  from  glands  in  the  abdomen, 

116 


THE  ARACHNIDS  AND   THE  MYRIAPODS       117 


which  secrete  a  viscous  fluid  that  hardens  into  silk  on 
exposure  to  the  air.  Two  trachece  (Fig.  58,  8),  which  give  off 
branches  to  different  parts  of  the  abdomen,  open  just  in  front 
of  the  spinnerets. 

Many  spiders  build  circular 
webs  of  silk,  in  which  they  cap- 
ture insects  to  suck  their  blood. 
A  common  species  of  garden 
spider  (Argi'ope  ripa'ria)  is  shown 
in  Fig.  59.  The  spider  first  spins 
a  line  across  the  space  where  the 
web  is  to  be,  and  then  attaches 
near  its  center  other  threads, 
which  it  carries  to  different  points, 
making  the  radiating  foundation- 
lines  of  the  web.  These  lines  are 
all  dry  and  inelastic.  Concentric 
spiral  lines  of  an  adhesive  nature 
are  then  added,  the  hind  legs 
being  used  to  place  the  threads, 
and  an  oval  cover  of  silk  is  spun 
in  the  center,  beneath  which,  or  FlG  5g  External  Anatomy  of  th 

'  f*       "I     ~1  1       1  P  j  1  "Til 


Spider  (Epeira  vulgaris). 
larged.    (After  Emerton) 


ie 

En- 


in  a  folded  leaf  at  the  side,  the 
spider  lurks  in  watch  for  its  prey. 
A  zigzag  band  of  white  silk  cross- 
ing the  center  is  usually  added 
to  strengthen  the  web.  When 
an  insect  is  captured  the  spider 
rushes  out,  and  if  there  is  any 
danger  of  the  escape  of  the  prey,  it  is  deftly  wound  with 
more  silk  till  its  struggles  have  ceased.  If  it  proves  to  be  a 
wasp  or  other  dangerous  capture,  or  if  it  is  too  big  to  be 
safely  managed,  it  is  often  assisted  to  escape  by  cutting  the 
web,  which  is  then  repaired  for  another  victim. 


1,  cephalothorax;   2,  abdomen;   3, 
fourth  leg;  4,  mandible;  5, palpus; 

6,  opening  to  breathing-organ ; 

7,  openings    to    reproductive 
organs;  8,  trachea;;  9,  spinnerets 
(3  pairs) ;  10,  anus 


118 


GENERAL  ZOOLOGY 


Like  the  click-beetles  and  many  others  of  the  Coleoptera, 
this  spider  when  alarmed  has  the  habit  of  dropping  to  the 

ground   as   if    dead.     It   spins   a 
thread  of  silk  as  it  drops ;  when 


FIG.  59.  Garden-Spider  and  Web. 
Reduced 

the  danger  is  over  it  is  able  by  this  means 
to  find  its  way  back  to  the  iveb. 

The  eggs  are  laid  in  the  autumn  in  a  sac  of  silk  (Fig.  60), 
which  may  contain  from  five  hundred  to  two  thousand  eggs. 
These  eggs  hatch  early  in  the  winter,  and  the  young  live  in 
the  case  through  the  cold  weather,  feeding  on  each  other,  so 
that  by  spring  a  comparatively  small  number  of  spiders 


THE  ARACHNIDS  AND   THE  MYRIAPODS       119 


emerge.    By  successive  molts,  without  marked  metamorphosis, 

they  reach  their  adult  size. 

The   dark-colored,   hairy   spiders    (Lyco'm)    found    under 

sticks  and  stones  usually  build  tubular  nests  in  the  ground, 

which  they  line  with  silk.    They  do  not 

make  a  web   to   capture  their  prey,  but 

spring  upon  it  as  they  run  about  in  search 

of  food.    The  females  may  often  be  seen 

dragging  after  them  the  large  gray  ball 

which  contains,  at   first,  their  eggs,  and 

afterwards    the    young.    After  a    certain 

time  the  young  leave  the  silken  case,  and 

for  some  time  longer  run  about  over  the 
body  of  the  mother. 

These  spiders  are 
often  called  tarantulas, 
but  that  name  should  be 
restricted  to  the  large, 
hairy  spiders  of  the 
warm  parts  of  the  world, 
which  can  be  distinguished  from  all  other 
spiders  by  the  fact  that  the  terminal  seg- 
ment of  the  mandibles  works  vertically 
instead  of  horizontally.  Tarantulas  are 

universally  dreaded  in  the  countries  where 
FIG.  01.  Trap-Door  ,  ,  .  . 

Spider  Burrow,  theJ  grow  to  be  of  large  Slze>  and  theJ  are 
showing  Side  Tube,  believed  to  be  very  poisonous.  The  ability 
Reduced.  (After  of  ider  to  •  tl  human  skin 

Emerton)  \ 

depends,  of  course,  on  its  size  and  the 
strength  of  its  jaws ;  the  effect  produced  by  the  bite  depends 
not  only  on  the  amount  of  poison  injected  into  the  wound 
but  also  on  the  age  and  mental  and  physical  condition  of 
the  person  bitten.  Though  many  stories  of  death  by  taran- 
tula bites  have  been  told,  most  of  them  are  clearly  untrue. 


FIG.  60.  Egg-Case  of 
the  Garden-Spider. 
Natural  size.  (After 
Wilder) 


120 


GENERAL  ZOOLOGY 


Persons    have    been    bitten    by    them,    and    only  temporary 
pain  and  swelling  have  resulted,  something  like  that  which 

follows  the  sting  of  a  bee. 

Among  the  most  interesting  of 
the  tarantula  family  are  the  trap- 
door spiders  of  the  western  and 
southern  states,  and  of  southern 
Europe.  They  build  burrows, 
Avhich  they  line  with  silk,  and 
provide  with  a  lid  lined  with  silk, 
attached  by  one  edge  to  the  mouth 
_of  the  burrow.  A  European  spe- 
„  cies  builds  a  nest  with  a  side  tube 
(Fig.  61)  into  which  it  can  retreat 

Fio.62.  .lumping-Spider.  Enlarged.   -     i{         of  danger,  closing  a  door 
(After  Peckham)  '  5 

at  the  entrance  ot  this  tube. 

The  jumping-spiders  (As'tia  vittata,  Fig.  62)  may  be  recog- 
nized by  the  stout,  hairy  body  and  the  square  head.  They  are 
usually  conspicuously  colored,  and  have  bright,  staring  eyes. 
They  build  no 
webs  to  capture 
their  prey,  but 
spring  upon  it, 
often  from  a 
considerable 
distance.  These 
spiders  are 
interesting  on 
account  of  the 
remarkable  an- 
tics which  the 
males  perform  before  the  females.  Dr.  and  Mrs.  Peckham, 
in  their  study  of  the  habits  of  this  group,  say  :  "  The  fact 
that  the  males  vie  with  each  other  in  making  an  elaborate 


FIG.  63.   Harvestman.    Natural  size 


THE  ARACHNIDS  AND  THE  MYRIAPODS       121 


display  not  only  of  their  grace  and  agility  but  also  of  their 
beauty  before  the  females,  and  that  the  females  after  atten- 
tively watching  the  dances  and  tournaments  which  have  been 
executed  for  their  gratification,  select  for  their  mates  the 
males  that  they  found  most  pleasing,  points  strongly  to  the 
conclusion  that  the  great  differences  in  color  and  in  ornament 
between  these  spiders  are  the  result  of  sexual  selection." 

Harvestmen.  The  long-legged  harvestmen,  or  daddy-long- 
legs (Liolu'num,  Fig.  63),  are  allied  to  the  spiders.  They 
can  be  recognized  by  the  eight  extremely  long  legs,  which  are 
thus  developed  as  organs  of  touch,  as  well  as  for  walking. 
They  are  harmless  creatures,  found  in  damp  and  shady  places  ; 
they  feed  on  small  insects,  especially  aphids. 

Mites  and  Ticks.  The  mites  and  ticks  are  related  to  the 
harvestmen  and  to  spiders.  They  show  less  segmentation  of 
the  body  than  the  preceding  groups.  They  are  small,  oval, 
eight-legged  forms.  The  mouth-parts  are  more  or  less  united 
to  form  a  beak.  Some  are  parasitic  on  other  animals  (Ixo'des, 
Fig.  64) ;  others, 
like  the  common 
red  mite  which  in- 
fests house-plants,  t&^^&^S&.M-  A 
suck  the  fluids  of 
vegetation.  One  of 
them  produces  the 
disease  known  as 
mange,  among 

dogs,    horses,    and    FIG.  04.    Cattle-Tick.    Enlarged.    (After  Howard, 
COWS.  Year-book,  Department  of  Agriculture,  1891) 

Scorpions.  The 
scorpions  have  the 
body  plainly  segmented.  In  the  common  scorpion  (Bu'thus, 
Fig.  65),  found  under  sticks  in  our  southern  states,  the 
maxillae  are  greatly  elongated,  making  a  formidable-looking 


A,  parasite  without  food ;  B,  parasite  rilled  with  blood 
from  host 


122 


GENERAL  ZOOLOGY 


pair  of  claws.    The  abdomen  is  provided  with  a  sting  at  its 
extremity.    The  whip-scorpion  (Thelyph'onus),  also  found  in 

similar  situations  in  the  South, 
is  another  formidable -looking 
creature,  with  immensely  devel- 
oped maxillse,  which  are  used 
to  pull  open  decaying  wood  in 
search  of  small  insects,  which 
form  its  food.  Its  appearance 
accounts  for  the  dread  it  in- 
spires, but  there  is  no  evidence 
to  show  that  it  is  harmful  to 
man. 

Definition  of  Arachnida  (Gr. 
arachne,  spider).  All  the  forms 
considered  so  far  in  this  chapter 


FIG.  65.  Photograph  of  Scorpion,  belong  to  the  class  Arach'nida. 
Natural  size.  (American  Museum  The  Arachnida  a^ree  in  having 
of  Natural  History)  , ,  .,  „  ,fo.  4 

the  somites  iused  into  two  more 

or  less  clearly  marked  regions,  the  cephalothorax  and  the 
abdomen.  There  is  no  distinct  head,  as  in  insects.  Eight 
legs  are  present.  The  Arachnida  undergo  no  well-marked 
metamorphosis. 

Centipeds.  The  common  centiped  (Litho'bius,  Fig.  66)  found 
under  the  bark  of  trees  is  an  elongate,  flattened  animal, 
with  long  antennae,  many  somites,  and  a  pair  of  legs  on  every 
somite.  There  is  a  poison-gland  in  the  base  of  the  first  pair 
of  legs,  which  is  used  to  kill  earthworms  and  insects,  upon 
which  Lithobius  feeds.  The  female  is  furnished  with  two 
hooks  at  the  end  of  the  body  close  to  the  oviduct.  When  an 
egg  is  laid  it  is  seized  by  these  hooks  and  rolled  over  till  it 
is  completely  covered  with  earth,  which  adheres  to  the  egg 
on  account  of  a  sticky  substance  with  which  it  is  covered. 
It  has  been  observed  that  if  a  male  Lithobius  perceives  the 


THE  ARACHNIDS  AND  THE  MYRIAPODS       123 

egg   before    it  is    disguised   by    the    covering    of  earth,  he 
attempts  to  seize  and  devour  it. 

Centipeds  are  widely  distributed  over  the  world.  In  the 
tropics  they  grow  to  be  over  thirty  centimeters  (one  foot) 
long.  Some  species  are  poisonous,  even  to  man,  and  death 
has  been  known  to  result  from  their  bite.  They  are  active 


•--rC* 


FIG.  06.    Centiped  and  Milleped.    Reduced 

creatures,  and  feed  on  living  animals.  The  number  of  somites 
varies  from  about  nine  to  over  two  hundred.  A  pair  of  legs 
is  attached  to  each  somite.  The  following  lines  were  written 
by  Professor  E.  Ray  Lankester,  of  England,  after  an  attempt 
to  study  the  order  in  which  the  legs  were  moved. 

A  centipede  was  happy  quite 

Until  a  toad  in  fun 

Said,  "  Pray,  which  leg  moves  after  which  ?  " 

This  raised  her  doubts  to  such  a  pitch, 

She  fell  exhausted  in  the  ditch, 

Not  knowing  how  to  run. 


124  GENERAL  ZOOLOGY 

Millepeds.  Other  elongate  forms  called  millepeds  (Spirob'- 
olus.  Fig.  66)  may  be  distinguished  from  the  centipeds  by  the 
more  cylindrical  body.  Millepeds  also  possess  a  greater  num- 
ber of  legs  than  centipeds,  each  somite,  with  the  exception  of 
several  coming  directly  after  the  head,  apparently  bearing  two 
pairs  of  legs.  They  live  in  damp  places  and  feed  on  living  or 
decaying  vegetable  matter ;  they  are  entirely  harmless.  Many 
have  the  power  of  coiling  themselves  up  when  disturbed. 
The  larvae,  when  first  hatched,  have  few  somites,  and  but 
three  pairs  of  legs. 

Definition  of  Myriapoda  (Gr.  myria,  many ;  pous,  foot). 
The  centipeds  and  millepeds  are  included  in  the  class  Myri- 
ap'oda.  Myriapods  are  distinguished  from  insects  and  arach- 
nids by  the  greater  number  of  somites  and  appendages.  They 
breathe  through  spiracles  placed  along  the  sides  of  the  body. 
After  hatching  from  the  egg,  the  young  develop  without  any 
marked  metamorphosis.  It  is  likely  that  centipeds  and  mille- 
peds are  not  in  reality  as  closely  allied  as  might  seem  from 
the  external  appearance. 


OF  THF 

UNIVERSITY  j 

OF  ,>, 


CHAPTER  Xll 
THE  CRAYFISH 

All  night  the  crawfish  deepens  out  her  wells, 

As  shows  the  clay  that  freshly  curbs  them  round. 

J.  P.  IRVINE,  Summer  Drought. 

Habitat  and  Distribution.  Crayfishes,  also  called  crawfishes, 
are  found  in  bodies  of  fresh  water  on  every  continent  except 
Africa,  and  in  many  of  the  large  islands.  The  eastern 
American  species,  Cam'barus  af 'finis  (Fig.  67),  which  grows  to 
the  length  of  live  or  six  inches,  may  be  taken  as  an  example 
of  the  several  genera  and  the  m'any  species  which  are  known 
by  the  common  name  crayfish. 

External  Plan  of  Structure.  The  body,  except  for  the 
ventral  surface  of  the  abdomen,  is  covered  with  a  thick  wall, 
formed,  like  the  covering  of  insects,  from  the  hardening  of  a 
secretion  of  the  outer  layer  of  the  skin.  Unlike  the  insects, 
this  protecting  sheath  is  filled  with  carbonate  of  lime.  The 
body  is  divided  into  a  cephalothorax  and  abdomen  (Fig.  67, 1, 2), 
as  in  the  arachnids.  There  are  no  indications  on  the  dorsal 
surface  of  separate  somites  in  the  cephalothorax,  but  on  the 
ventral  surface  transverse  grooves  and  paired  appendages 
indicate  a  division  into  thirteen  somites.  The  abdomen 
(Fig.  67,  2)  plainly  consists  of  seven  somites,  of  which  the 
first  six  bear  jointed  appendages.  The  external  plan  upon 
which  the  crayfish  is  formed  is  similar  to  that  of  the  insects, 
arachnids,  and  myriapods ;  that  is,  a  series  of  somites  placed 
one  after  the  other,  with  all  appendages  jointed  or  segmented. 

The  Cephalothorax.  The  shell  covering  the  dorsal  and 
lateral  surfaces  is  distinct  from  the  hard  parts  elsewhere  on 
the  body,  and  is  termed  the  carapace.  At  the  anterior  dorsal 

125 


126 


THE  CRAYFISH  127 

end  of  the  carapace  there  is  a  prominent  beak,  or  rostrum 
(Fig.  67,  3),  beneath  which,  on  either  side,  extends  an  eye 
(Fig.  ,67,  4),  borne  on  a  stalk.  Study  of  the  living  crayfish 
enables  one  to  see  how  well  the  rostrum  protects  the  stalked 
movable  eye.  The  eye  is  compound  ;  the  manner  in  which 
the  image  is  formed  is  practically  the  same  as  in  the  insects. 
Crayfishes  have  no  simple  eyes. 

The  cephalothorax  bears  at  its  anterior  end  six  slender, 
many-jointed  feelers, the  shortones  calledawfew>m?e«  (Fig.  67,6), 
the  long  ones,  antennce  (Fig.  67,  6).  The  four  antennules  are 
really  the  two  branches  of  a  single  pair  of  appendages  coming 
from  a  short  stem  which  is  attached  to  the  body.  On  the 
upper  surface  of  one  of  the  segments  of  this  stem  is  a  small 
hole  surrounded  by  a  number  of  bristles.  The  hole  opens  into 
a  cavity  which  contains  several  small  grains  of  sand  placed 
there  by  the  crayfish  itself  after  every  molt.  (The  process  of 
molting  is  explained  in  Chapter  XIII.)  This  organ,  with 
its  nerve-connections,  constitutes  the  "  ear "  of  the  crayfish 
(Fig.  67,  7),  the  chief  function  of  which  is  to  help  the  ani- 
mal to  balance  itself  during  locomotion.  The  technical  name 
otocyst  is  given  to  it.  The  antennae  are  the  inner  branch  of  a 
pair  of  double-branched  appendages,  of  which  the  outer  branch 
is  short,  flat,  and  triangular,  and  lies  just  below  the  eyes,  where 
it  serves  a  protective  function.  It  is  called  the  squame.  On 
the  lower,  or  basal,  segment  of  the  stem  of  this  pair  of  append- 
ages is  a  small,  hard,  round  swelling,  or  papilla  (Fig.  67,  8; 
Fig.  68,  II,  l),  on  which  is  the  opening  from  the  "kidney,"  or 
green-gland,  shown  in  broken  outline  in  Fig.  67. 

About  the  mouth  are  six  pairs  of  appendages.  The  first, 
the  hard  mandibles  (Fig.  67,  9),  are  adapted  to  crushing  into 
smaller  bits  the  food  seized  by  the  large  claws.  Each  mandi- 
ble bears  a  short  palpus  (Fig.  68,  III,  2).  Next  in  the  series 
are  the  first  and  second  maxillce  (Fig.  68,  IV,  V)  and  the  first, 
second,  and  third  maxillipeds  (Fig.  68,  VI,  VII,  VIII).  The 


128  GENERAL  ZOOLOGY 

maxillipeds  help  to  hold  the  food  in  place  at  the  mouth ;  the 
maxillse  also  assist  in  this,  and  probably,  with  the  upper 
and  lower  lip  and  the  wall  of  the  mouth-cavity,  are  the  seat 
of  the  sense  of  taste.  The  second  pair  of  maxilla}  also  act 
as  "gill-bailers  "  (Fig.  68,  V,  3-4  ;  Fig.  69,  1),  which,  by  their 
motion,  help  to  maintain  a  current  of  water  in  the  gill-chamber 
(Fig.  69,  5),  thus  providing  oxygen  for  respiration.  In  the 
maxillipeds  a  basal  stem,  with  two  branches  arising  from  it, 
can  be  easily  distinguished.  The  separation  between  head 
and  thorax  is  understood  to  come  between  the  second  maxillae 
and  the  first  maxillipeds,  thus  making  five  pairs  of  append- 
ages in  the  head-region. 

After  the  maxillipeds  the  next  thoracic  appendages  are  the 
large  claws,  or  chelipeds  (Fig.  67,  11),  composed  of  seven  seg- 
ments, of  which  the  last  two  from  the  body,  or  distal  two, 
are  adjusted  to  form  a  nipper,  with  which  the  animal  captures 
and  holds  even  rapidly  swimming  fishes.  The  remaining 
thoracic  appendages  are  the  four  pairs  of  walking-legs  (Fig.  67, 
12 ;  Fig.  68,  XI,  XII),  also  composed  of  seven  segments,  the  first 
two  pairs  with  nippers  at  their  ends,  and  the  last  two  pairs 
without  nippers.  The  three  pairs  of  maxillipeds,  the  one  pair 
of  chelipeds,  and  the  four  pairs  of  walking-legs  constitute  the 
eight  pairs  of  appendages  of  the  thorax. 

The  Abdomen.  There  are  six  pairs  of  appendages  on  the 
abdomen.  The  first  abdominal  appendages  of  the  female  are^ 
small,  single,  and  thread-like ;  in  the  male  (Fig.  67,  13),  they 
are  long  and  rigid,  differing  considerably  from  all  the  others 
except  the  second  pair  (Fig.  67,  14).  The  second  abdominal 
appendage  in  the  female  is  like  the  third. '  The  third,  fourth, 
and  fifth  pairs,  called  swimmerets  (Fig.  67,  15),  are  alike  in 
both  sexes.  The  pair  of  appendages  of  the  sixth  somite 
(Fig.  67,  16)  are  made  up  of  broad  flat  branches  jointed  to 
a  short  thick  stem,  and  form,  with  the  last  somite,  called 
the  telson  '(which  is  without  appendages),  a  strong  tail-fin. 


4     XI 


FIG.  68.  Appendages  of  the  Crayfish  (Cambarus  affinis),  from  the 

left  side.     Natural  size. 
(I,  II,  III,  etc.,  stand  for  the  number  of  the  somite  in  the  animal's  body) 

1,  protopodite;  2,  eudopodite;  3,  exopodite;  4,  epipodite  with  gill-filaments; 
5,  gill  with  gill-filaments 

129 


130  GENERAL  ZOOLOGY 

By  doubling  underneath  it  is  capable  of  striking  hard  blows 
against  the  water  and  forcing  the  crayfish  suddenly  backward. 
A  basal  stem  with  two  branches  is  to  be  clearly  seen  in  all 
the  abdominal  appendages  except  the  first  pair  in  the  female. 

Homology  and  Analogy.  The  fact  that  a  stem  and  two 
branches  are  apparent  in  several  appendages  which  have  been 
mentioned,  is  important  enough  to  deserve  further  discussion. 
The  simplest  condition  of  the  branched  appendage  is  seen  in 
the  third,  fourth,  and  fifth  abdominal  appendages  (Fig.  68,  XVI). 
If  the  branches  are  spread  slightly,  the  form  resembles  the 
capital  letter  Y.  Taking  a  swimmeret  as  a  model,  the  stem, 
which  is  termed  the  protopodite  (Fig.  68,  XVI,  1),  is  seen  to  be 
made  up  of  a  short  basal  segment,  the  coxopodite^  and  a  long 
segment,  the  basipodite.  Of  the  two  branches,  the  one  nearest 
the  median  line  of  the  body  is  the  endopodite  (Fig.  68,  XVI,  2); 
the  outer  is  the  exopodite  (Fig.  68,  XVI,  3).  Wherever  in  the 
series  of  appendages  we  find  a  stem  and  two  branches,  the 
protopodite  corresponds  to  the  protopodite  of  all  the  other 
appendages  of  the  series,  —  and  so  with  the  endopodites  and 
the  exopodites. 

The  legs  seem  to  be  formed  on  a  different  plan,  but  we 
know  from  the  embryology  (the  science  of  the  early  stages 
of  development)  of  the  crayfish  that  while  the  egg  is  still 
unhatched  the  embryo  has  legs  that  have  two  branches  (com- 
pare larval  lobster,  Fig.  70),  and  that  the  outer  and  smaller 
one  disappears  before  the  embryo  hatches.  The  first  and 
second  'maxillae  have  the  parts  of  a  typical  crayfish  append- 
age, divided  as  shown  in  Fig.  68,  IV,  V.  The  crushing  part 
of  the  mandible  is  thought  to  represent  the  coxopodite  and 
basipodite  combined.  The  little  palpus  is  the  endopodite; 
the  exopodite  is  missing  in  the  adult. 

In  this  brief  description  of  the  appendages  of  the  crayfish 
two  very  important  facts  in  morphology  (the  science  of  form) 
have  been  suggested.  One,  the  inherent  similarity  of  structure 


THE  CRAYFISH  131 

of  the  parts  of  the  appendages  in  a  series ;  the  other,  a  diver- 
gence in  the  forms  of  appendages  because  of  adaptations  to 
different  uses.  Perhaps  no  fact  in  nature  is  better  known 
than  the  fact  that  organs  are  adapted  in  general  form  and  in 
special  parts  to  perform  particular  functions.  It  is  only  when 
we  come  to  examine  a  series  of  organs  like  the  appendages  of 
the  crayfish  that  we  obtain  some  insight  into  the  very  great 
changes  which  must  often  take  place  before  organs  become 
adapted  to  the  performance  of  even  slightly  different  func- 
tions. Morphologists,  realizing  the  extent  of  the  principle  of 
adaptation,  have  been  able  to  show  that  in  a  series  of  organs, 
like  the  appendages  of  the  crayfish,  any  part  of  an  appendage, 
as,  for  example,  the  endopodite,  can  be  shown  to  correspond  to 
the  endopodite  in  all  the  other  appendages,  no  matter  what 
the  superficial  differences  may  be. 

In  referring  to  these  corresponding  parts  we  use  the  tech- 
nical term  "  homologous  parts."  The  protopodites  of  all  the 
appendages  are  structurally  similar ;  that  is  to  say,  they  are 
situated  in  the  same  relation  to  adjacent  parts  all  through 
the  series.  Likewise  the  legs  and  the  antennse,  being  inner 
branches  (endopodites),  and  being  jointed  to  the  second  seg- 
ment of  the  appendages,  are  homologous  parts.  If  such  unlike 
parts  as  the  antenna;  and  the  legs  are  homologous,  it  is,  of 
course,  very  clear  that  the  legs  and  the  chelipeds  are  homolo- 
gous as  whole  endopodites,  and  also  segment  by  segment  from 
the  base  to  the  tip.  The  crayfish  appendages  are  examples  of 
serial  homology ;  in  a  broader  sense,  homology  deals  with 
organs  of  all  sorts  that  have  a  corresponding  position  and  origin 
in  different  animals.  In  connection  with  the  study  of  homol- 
ogy, the  science  of  structurally  similar  parts,  we  find  the  word 
"  analogy  "  in  frequent  use.  The  difference  between  homolo- 
gous parts  and  analogous  parts  is  one  easily  made  clear  by 
applying  the  terms  to  the  present  study.  The  legs  of  cray- 
fishes are  analogous  parts,  because  their  use  is  the  same ;  they 


132  GENERAL  ZOOLOGY 

are  homologous  parts  because  they  are  structurally  similar. 
The  same  is  true,  to  take  another  case,  of  the  swimmerets  of 
the  third,  fourth,  and  fifth  abdominal  somites ;  but  whereas  the 
antenna  and  the  legs  are  homologous,  they  are  not  analogous, 
because  their  functions  are  different.  Ordinarily,  zoologists 
use  the  word  "  analogous  "  in  a  little  different  way  from  that 
suggested  above.  Instead  of  being  applied  to  structures  in 
the  same  animal,  it  is  most  commonly  applied  to  organs  of 
similar  function  in  different  animals ;  for  example,  the  wings 
of  insects  and  birds,  —  organs  which  have  the  same  use  but 
are  not  homologous. 

The  Digestive  System.  The  mouth  (Fig.  67,  17)  of  the  cray- 
fish is  located  between  the  two  mandibles.  Reference  to 
Fig.  67,  18,  will  give  an  idea  of  the  length  of  the  oesoph- 
agus and  the  position  and  relative  size  of  the  stomach 
(Fig.  67,  19).  The  latter  has  two  more  or  less  clearly  marked 
'  regions,  —  the  anterior  enlarged  region  and  the  posterior 
funnel-shaped  space.  As  the  food  passes  into  the  anterior 
portion  the  unbroken  bits  are  caught  between  the  contig- 
uous grinding  surfaces  of  three  hard  processes  (Fig.  67,  20) 
extending  from  the  stomach-wall.  These  three  "teeth" 
one  in  the  median  dorsal  line  and  two  at  the  sides  —  together 
constitute  the  "  gastric  mill."  Muscles  attached  to  them  and 
to  the  inner  surface  of  the  carapace,  by  contracting,  perform 
the  operation  of  grinding.  The  posterior  part  of  the  stomach 
is  filled  with  slender  filaments  which  extend  from  the  wall 
out  into  the  cavity  (Fig.  67,  21).  These  filaments  prevent  the 
unbroken  particles  of  food  from  passing  through  into  the 
intestine,  allowing  only  the  thoroughly  ground-up  food  to 
do  so.  Absorption  does  not  occur  in  either  division  of  the 
stomach /but  in  the  intestine  (Fig.  67,  24),  which  extends 
straight 'from  the  stomach  to  the  ventral  surface  of  the  tel- 
son.  A  pair  of  digestive  glands  (Fig.  67,  23)  lie  one  on  either 
side  of  the  stomach  and  intestine.  They  open  by  tubes  into 


THE   CRAYFISH 


133 


the  posterior  division  of  the  stomach,  and  have  the  combined 
functions  of  digesting  food  and  absorbing  some  of  the  prod- 
ucts of  digestion. 

The  Circulatory,  Respiratory,  and  Excretory  Systems.  The 
heart  (Fig.  67,  26)  is  a  muscular  organ  lying  beneath  the  dor- 
sal body-wall  posterior  to  the  stomach.  The  blood  finds  its 
way  into  the  heart  through  three  pairs  of  openings  furnished 
with  valves  to  prevent  the  escape  of  blood.  When  the  heart 
contracts  the  blood  flows  both  forward  and  backward  at  the 


FIG.  69.  Gill-Chamber  and  Gills  of  the  Crayfish  (Cambarus  affinis). 
Slightly  enlarged 

1,  gill-bailer  on  second  maxilla;  2,  first  maxilliped;  3,  second  maxilliped  with 
first  outer  gill;  4,  sixth  outer  gill;  5,  last  gill  of  inner  series 

same  time,  forward  by  five  tubes  and  backward  by  two  tubes, 
called  arteries  (Fig.  67,  29,  30,  31).  These  arteries  branch  into 
many  smaller  vessels  with  open  ends  ;  from  the  open  ends 
the  blood  flows  over  the  tissues  of  the  body  in  sinuses,  all  of 
which  connect  with  a  still  larger  median  cavity,  the  ventral 
sinus,  lying  along  the  ventral  wall  of  the  thorax  and  abdomen. 
Branches  from  the  median  ventral  sinus  extend  out  into  the 
gills.  The  blood  is  carried  back  to  the  base  of  the  gills  by 
parallel  channels,  and  finally  carried  lip  to  the  pericardial 
sinus  in  which  the  heart  lies.  The  set  of  delicate,  plume-like 


134  GENERAL   ZOOLOGY 

gills  (Fig.  69,  4)  are  attached  to  and  near  the  basal  joints  of 
the  thoracic  appendages,  and  extend  dorsally  into  partially 
closed  chambers  bounded  by  the  body-wall  on  the  inside  and 
the  ventral  extension  of  the  carapace  on  the  outside.  Since 
it  is  sometimes  necessary  for  the  crayfish  to  make  journeys 
from  pond  to  pond  in  dry  seasons,  the  gills  are  thus  protected 
from  sudden  drying.  Water  is  drawn  into  and  out  of  this 
gill-cavity  by  means  of  the  action  of  the  gill-bailers  on  the 
second  maxillae  already  referred  to  (Fig.  68,  V,  3-4 ;  Fig.  69,  1). 
The  blood  flowing  into  the  gills  from  the  ventral  sinus  gives  up 
its  carbon  dioxide  waste  and  receives  oxygen  from  the  water. 

The  green-glands  are  prominent  organs  (Fig.  67,  8)  in  the 
ventral  region  of  the  body-cavity  in  the  head.  A  large  artery 
carries  blood  to  them,  and  nitrogenous  waste  matter  is  sepa- 
rated by  them  from  the  blood' and  finds  its  way  to  the  opening 
on  the  basal  segment  of  the  antennae. 

The  Nervous  and  Muscular  Systems.  The  "brain,"  the 
supraoesopliageal  ganglion,  of  the  crayfish  is  a  mass  of  nervous 
tissue  resulting  from  the  aggregation  of  several  pairs  of  ganglia 
(Fig.  67,  33).  Pairs  of  nerves  may  be  traced  to  the  eyes,  the 
antennas,  and  the  antennules.  Two  slender  connectives,  simi- 
lar to  those  described  for  the  locust,  extend  from  the  brain, 
encircle  the  oesophagus,  and  join  the  sulxxsopliageal  ganglion 
(Fig.  67,  34)  posterior  to  the  mouth.  This  ganglion,  too,  is 
really  a  combination  of  several  pairs  of  ganglia,  which  send 
off  the  nerves  to  some  of  the  head  somites  and  to  some  of  the 
thoracic  somites.  There  are  five  other  ganglia  in  the  thorax 
joined  to  each  other  (first  thoracic  ganglion,  Fig.  67,  35),  and  to 
the  six  ganglia  in  the  abdomen,  by  the  double  nerve-cord  which 
is  a  continuation  of  the  connectives  that  encircle  the  oesophagus. 

The  muscles  of  the  abdomen  are  arranged  in  a  very  com- 
plicated fashion  and  are  capable  of  powerful  action.  In  all 
parts  of  the  body  muscles  are  attached  to  the  inner  surface 
of  the  exoskeleton. 


THE  CRAYFISH  135 

The  Reproductive  System.  The  male  reproductive  organ, 
the  spermary  (Fig.  67,  37),  and  the  female  reproductive  organ, 
the  ovary,  lie  just  below  the  heart ;  each  consists  of  a  three- 
lobed  organ.  In  the  male  a  sperm-duct  (Fig.  67,  38)  leads  from 
either  side  of  the  spermary  to  an  opening  (Fig.  67,  39)  on  the 
basal  segment  of  either  fourth  walking-leg.  In  the  female  the 
oviducts  lead  to  similar  openings  on  the  second  walking-leg. 

Development.  Cambarus  affinis  lays  its  eggs  in  the  spring. 
Most  species  of  crayfishes  lay  their  eggs  then.  The  princi- 
pal burrowing  species,  Cambarus  diog'enes,  lays  its  eggs  in 
April  and  they  hatch  in  May,  while  a  river  species,  Cambarus 
immu'nis,  lays  its  eggs  in  the  fall  and  they  hatch  in  the  fol- 
lowing spring.  When  the  egg-lay  ing  season  arrives  the  male 
deposits  spermatozoa  in  a  shallow  cup  called  the  annulus,  on 
the  ventral  surface  of  the  female,  between  the  fourth  pair  of 
legs.  The  mass  of  spermatozoa  stays  in  the  annulus  till  the 
female  lays  her  eggs.  It  is  not  certain  how  long  the  sper- 
matozoa lie  there  before  the  eggs  are  laid.  However,  when 
the  eggs  are  discharged  from  the  oviduct  they  pass  back  over 
the  mass  of  spermatozoa.  Fertilization  is  accomplished  when 
a  spermatozoon  enters  an  egg.  The  fertilized  eggs  are  carried 
back  and  fastened  to  the  swimmerets  by  a  glutinous  substance. 
There  the  embryos  develop,  and  the  larvae,  when  they  hatch, 
remain  clinging  to  the  female's  swimmerets  by  their  cheli- 
peds  for  some  time,  probably  several  weeks. 

Relation  to  Environment.  Crayfishes  live  in  a  great  variety 
of  places.  They  are  fresh- water  animals,  but  one  species  has 
also  been  found  in  the  sea.  As  a  rule,  they  crawl  on  the 
bottom  of  rivers,  brooks,  and  ponds,  concealing  themselves  in 
crevices  or  under  protecting  pieces  of  rock  or  submerged  logs. 
Several  species  make  burrows  in  the  soft  earth  of  meadows. 
The  most  widely  distributed  of  these  is  Cambarus  diogenes. 
Species  which  live  in  ponds  that  are  likely  to  dry  up  in  the 
summer,  and  also  a  few  that  live  in  rivers,  leave  the  water 


136  GENERAL  ZOOLOGY 

in  summer  and  burrow  into  the  earth  until  they  come  to 
water.  At  the  bottom  of  their  burrows,  sometimes  three  feet 
from  the  surface,  they  dig  out  a  flask-shaped  enlargement 
and  stay  in  it  or  near  it  till  the  next  spring.  The  chimneys 
made  at  the  top  of  the  "  wells,"  referred  to  in  the  quotation 
at  the  beginning  of  the  chapter,  are  made  by  the  burrowing 
crayfish  merely  as  an  incident  in  getting  rid  of  the  mud 
brought  from  below.  Sometimes  crayfishes  stop  up  their  bur- 
rows completely.  In  that  case  they  probably  remain  in  a 
dormant  condition  without  food  till  spring  returns.  In  the 
bed  of  a  pond  or  river  where  jutting  stones  abound  cray- 
fishes rest  with  the  abdomen  doubled  beneath  them  and  the 
head  toward  the  open.  Boys  often  lure  them  from  their 
hiding-places  with  a  piece  of  meat  tied  to  the  end  of  a 
weighted  string.  The  animal  invariably  seizes  the  meat  in 
a  cheliped,  and  usually  can  be  drawn  to  the  surface  before  it 
has  time  to  "  think  "  the  matter  over  and  let  go. 

The  distribution  of  crayfishes  is  directly  related  to  their 
power  of  adapting  themselves  to  conditions  of  considerable 
variability.  If  a  certain  definite  degree  of  temperature  or  of 
clearness  of  water  were  required,  they  would  be  restricted  to 
a  very  limited  area,  and,  indeed,  it  would  be  difficult  for 
them  to  maintain  themselves  at  all.  As  it  is,  we  find  them 
in  drinkable  water,  in  muddy  water,  in  sulphur-laden  water, 
and  in  sea-water,  but  never  in  the  water  of  streams  or  ponds 
of  a  country  devoid  of  limestone.  This  accounts  for  their 
absence  from  the  eastern  part  of  New  England,  where  the 
rocks  are  largely  of  granite. 

A  striking  example  of  adaptation  to  an  unusual  environ- 
ment is  found  in  the  cave-dwelling  crayfish,  Oambarus  pel- 
lu'cidus.  Professor  Eigenmann  of  Indiana,  Dr.  O.  P.  Hay 
of  New  York,  and  others  have  explored  the  caves  of  Indiana 
and  Kentucky  for  the  purpose  of  studying  the  animals  of 
their  subterranean  rivers.  The  blind  crayfish  has  small  and 


THE  CRAYFISH  137 

abortive  eyes,  but  its  sense  of  touch  is  developed  to  a  mar- 
velous degree  of  delicacy.  Dr.  Hay  says  that  although  the 
crayfishes  may  be  resting  quietly  on  the  bottom  of  a  rivulet, 
it  is  impossible  to  capture  them  with  a  net.  They  feel  the  jar 
in  the  water  and  dart  backward  with  great  accuracy  to  a  pro- 
tecting rock.  In  general  appearance  the  blind  crayfish  differs 
from  others  chiefly  in  having  an  exoskeleton  which  is  so  clear 
that  one  may  see  the  animal's  stomach  as  a  blue  mass  within, 
and  in  being  provided  with  antennae  longer  than  the  body. 

Crayfishes  are  eaten  by  fish  large  enough  to  swallow  them, 
and  they  in  turn  catch  small  fish  with  great  facility,  and  also 
insect  larvae,  snails,  tadpoles,  and  even  frogs.  They  have 
been  known  to  prey  upon  each  other,  and  also  to  eat  dead 
organic  matter ;  but  as  a  rule  they  eat  plant  and  animal  food 
in  the  fresh  condition. 

They  are  protected  by  their  hard  shells  from  the  attacks  of 
passing  fish.  The  color  of  the  shell  is  more  effective  still, 
since  whatever  the  color  of  the  bottom,  it  is  closely  imitated 
in  the  distribution  of  color  pigment  in  the  shell.  The  usual 
color  is  muddy  greenish-black  ;  in  ponds  where  the  mud  is 
bluish,  the  shell  is  also  blue.  An  account  has  been  written 
of  the  crayfishes  found  in  Sandy  Lake,  Pennsylvania,  where 
the  bottom  is  white  marl  and  clay.  All  the  crayfishes  which 
have  been  captured  in  the  pond  "  vary  in  color  from  almost 
pure  white  to  pink,  or  in  some  cases  to  a  delicate  greenish 
tint.  They  are  practically  invisible  when  at  rest.  The  fisher- 
men of  the  district  capture  them  and  use  them  for  bait  to 
catch  bass  in  other  lakes  where  the  bottom  is  of  dark  mud." 

In  America  crayfishes  seem  to  be  used  as  food  chiefly  by 
the  French  portion  of  our  population.  Possibly  the  rapid 
depletion  of  the  lobster  fisheries  may  cause  people  generally 
to  turn  to  the  lobster's  nearest  edible  relative.  In  France  the 
crayfish  industry  is  quite  extensive,  there  being  many  farms 
on  which  crayfishes  are  raised  for  the  market. 


CHAPTER  XIII 
THE  JOINTED-FOOT  ANIMALS:  ARTHROPODA 

The  Shelly  Crawlers  each  returning  year 

Cast  off  their  shells  and  new-made  Armour  wear. 

OPPIAX,  Ilalleutica. 

THE  ALLIES  OF  THE  CRAYFISH  :  CRUSTACEA 

The  Lobster.  Except  for  the  considerable  difference  in 
size,  and  the  slight  differences  in  the  shape  of  the  body, 
the  number  of  gills,  and  the  structure  of  abdominal  append- 
ages, the  description  of  the  adult  crayfish  would  serve  for  an 
account  of  the  structure  of  our  common  species  of  Ameri- 
can lobster,  Hom'arus  america'nus.  The  lobster  is  found  in 
greatest  numbers  along  the  coast  of  Maine  and  the  Canadian 
maritime  provinces.  Toward  the  south  the  number  gradu- 
ally decreases  to  the  Delaware  breakwater,  beyond  which 
they  are  very  rare.  In  their  days  of  greatest  abundance 
they  grew  to  be  about  sixty  centimeters  (two  feet)  in  length, 
weighing  twenty-five  pounds,  but  with  the  increase  in  the 
activity  of  the  lobster-fishing  industry  they  are  now  rarely  to 
be  found  weighing  over  two  pounds. 

The  lobster  lives  on  the  bottom.  It  is  protectively  colored, 
but  it  does  not  depend  wholly  upon  that  condition  for  escap- 
ing the  notice  of  its  enemies.  In  shallow  waters  lobsters  are 
known  to  conceal  themselves  beneath  masses  of  brown  sea- 
weed in  pits  and  holes,  and  also  to  find  safe  retreat  beneath 
jutting  ledges  of  rock,  where  they  rest  with  the  abdomen 
doubled  beneath,  ready  to  dart  out  and  seize  passing  prey  in 
their  claws.  We  have  no  way  of  knowing  the  exact  habits 
of  the  animal  when  at  its  greatest  depth  (a  hundred  fathoms), 

138 


THE  JOINTED-FOOT  ANIMALS  139 

but  since  its  enemies  are  probably  quite  as  persistent  there  as 
in  the  shallow  water,  every  means  of  defense  is  likely  to  be 
employed  to  the  utmost. 

The  lobster  is  capable  of  swimming  with  great  rapidity, 
by  suddenly  doubling  its  flexible,  muscular  abdomen  beneath 
and  shooting  backward  through  the  water.  The  habit  does 
not  appear  to  be  depended  on  except  to  enable  them  to  escape 
from  impending  danger.  Their  usual  mode  of  progression  is 
by  walking  on  the  tips  of  the  last  four  pairs  of  thoracic 
appendages,  the  chelipeds  being  extended  anteriorly,  appar- 
ently to  expose  as  little  of  their  bulk  to  the  water  as  possible. 
The  swimmerets  waving  in  rhythmic  motion  aid  the  animal 
in  its  movement  along  the  sea-bottom. 

With  all  their  appearance  of  armored  strength,  lobsters  are 
very  sensitive  to  changed  conditions  in  their  environment. 
When  captured  and  detained  in  "pounds  "  (artificially  inclosed 
spaces),  in  shallow  water,  they  will,  on  the  approach  of  win- 
ter, dig  burrows  in  the  sea-bottom  and  cover  themselves  all 
but  their  eyes  and  antennae.  There  they  remain  in  a  dor- 
mant condition  until  the  returning  warmth  of  spring  affects 
the  temperature  of  the  water.  In  their  natural  environment 
they  migrate  to  the  deep  waters  in  the  autumn  months  and 
remain  there  till  spring.  We  know  that  they  do  not  make 
burrows  and  lie  inactive  in  the  deep  waters,  because  fishermen 
catch  them  in  baited  traps  in  all  the  winter  months.  In  the 
winter  in  our  latitude  deep  waters  are  warmer  than  shallow 
waters;  in  summer  the  shallow  waters  are  warmer.  Lobsters 
are  sensitive  to  even  slight  changes  in  temperature.  In  the 
early  summer  they  have  been  known  to  return  to  deep  water 
immediately  on  the  occurrence  of  a  storm  in  the  atmosphere 
above  them.  Another  factor  which  must  operate  strongly  in 
determining  the  migration  to  the  shore  is  the  greater  supply 
of  food  there.  Lobsters  do  not  appear  to  migrate  up  and 
down  the  coast.  Hence,  if  all  the  lobsters  in  a  certain  bay 


140  GENERAL  ZOOLOGY 

and  vicinity  are  caught,  the  chances  are  against  that  region 
recovering  its  lost  supply. 

Slow,  inactive  animals  living  on  the  bottom  fall  an  easy 
prey  to  lobsters.  When  confined  in  pounds,  lobsters  even 
dig  up  clams  and  crush  the  shells  in  their  powerful  crush- 
ing claw,  which  is  the  thicker  one  of  the  two.  Fish  also  are 
caught,  even  where  both  captor  and  prey  have  perfect  free- 
dom of  action.  Those  who  have  studied  the  habits  of  lobsters 
closely  believe  that  although  the  lobster  is  a  scavenger  in 
the  sea,  it  nevertheless  prefers  living  food  to  dead  organic 
matter.  Seaweeds  form  part  of  their  food.  The  processes  of 
eating,  swallowing,  grinding  in  the  stomach,  and  digestion  are 
exactly  the  same  as  in  the  crayfish. 

Molting  in  the  lobster,  as  in  some  other  animals  with  a  hard 
exoskeleton,  is  an  extremely  important  and  critical  event, 
since  the  store  of  vitality  is  drawn  upon  in  preparation  for 
the  act  of  shedding  the  hard  armor,  and  in  fully  restoring  a 
protective  sheath.  In  the  act  of  molting,  the  lobster  does 
not,  as  a  rule,  split  the  dorsal  shell.  The  animal  bends,  mak- 
ing a  sharp  angle  at  the  junction  of  the  cephalothorax  and 
the  abdomen.  The  soft  body  at  that  point  begins  to  withdraw 
from  the  carapace.  Getting  out  of  the  rigid  shell  is  made  pos- 
sible by  a  preliminary  process  of  taking  up  into  the  blood  the 
lime  in  the  exoskeleton,  along  the  median  line  of  the  carapace, 
at  the  rostrum  or  beak,  and  at  the  narrow  joints  of  the  cheli- 
ped  and  walking-appendages.  The  blood  leaves  the  append- 
ages and  flows  into  the  sinuses  of  the  cephalothorax.  The 
withdrawal  of  the  cephalothorax  and  its  appendages  soon  fol- 
lows, and  lastly  the  abdomen  is  withdrawn  from  its  old  cover- 
ing, and  the  soft,  defenseless  lobster  conceals  itself  as  quickly 
as  its  weakened  condition  will  permit.  The  volume  and 
weight  rapidly  become  greater,  due  to  the  absorption  of  water. 
Later,  while  the  new  shell  formed  beforehand  under  the  old 
one  is  becoming  harder,  the  water  previously  absorbed  is 


THE  JOINTED-FOOT  ANIMALS 


141 


replaced  by  true  tissue.    This  periodic  growth  of  the  lobster 

really  begins  before  the  act  of  molting  takes  place;  in  fact, 

the  physiological  need  for  more  room  is  what  brings  about  the 

act  of  getting  rid  of  the  old  exoskeleton.    The  number  of 

molts  an  individual  lobster  may  have  depends,  in  a    great 

measure,  upon  the  abundance  of  its  food.     Males  molt  more 

frequently  than  females ;  hence  the  largest  lobsters  are  always 

males.   Very  young  lobsters  molt  more 

frequently  than  those  of  the  size  we 

find  in  the  market.    During  the  process 

of  molting  it  sometimes  happens  that 

an   appendage   is   broken  off.     In  the 

ordinary  course    of   its   life,   also,   the 

lobster  may  lose  a  claw  or  an  antenna. 

It  is  regenerated  in  two  or  three  molts 

after  the  accident.     The  crayfish  arid 

many  other  animals  closely  related  to 

these  two  have  the  same  power. 

The  female  lobster  lays  her  eggs 
usually  during  the  summer  months. 
The  eggs  remain  attached  to  the  swim- 
mere  ts  until  the  next  spring,  when 
the  embryos  hatch.  The  larval  lobster 
(Fig.  70)  immediately  floats  to  the  sur- 
face, and  for  several  weeks  swims  about 
there.  Its  length  at  first  is  about  eight  millimeters  (one  third  of 
an  inch).  In  general  appearance  it  resembles  the  adult  lobster, 
except  that  the  large  thoracic  appendages  are  two-branched 
and  the  abdomen  has  no  appendages.  After  the  sixth  molt  the 
lobster,  then  about  two  thirds  of  an  inch  long,  has  lost  the  outer 
branches  of  the  legs,  has  gained  abdominal  appendages,  and  is 
nearly  like  the  adult  in  other  respects.  At  about  this  time  the 
young  lobster  leaves  the  surface,  goes  to  the  bottom,  and 
makes  its  way  to  well-protected  places  near  the  shore. 


FIG.  70.  First  Larval  Stage 
of  American  Lobster, 
x  7.  (After  Herrick) 


142  GENERAL  ZOOLOGY 

The  commercial  value  of  the  lobster  is  very  great.  As  an 
article  of  human  food  it  is  fast  becoming  a  luxury.  Consid- 
ering its  original  abundance  at  times  when  a  fifteen-pound 
lobster  could  be  bought  at  the  fisheries  as  cheaply  as  a  two- 
pound  lobster,  that  is,  for  two  cents,  we  may  well  ask  whether 
it  is  not  time  for  the  ratification  of  treaties  between  the  United 
States  and  Canada  to  govern  more  effectively  the  activities 
of  persons  engaged  in  supplying  the  market.  The  researches 
of  Professor  Bumpus,  Professor  Herrick,  and  others,  have 
made  it  clear  that  a  female  lobster  seldom  lays  eggs  before 
she  is  at  least  eight  or  nine  inches  long.  Although  she  car- 
ries about  five  thousand  eggs  the  first  time,  two  years  later 
she  would  lay  many  thousand  more  than  that  number.  Be- 
cause of  the  numberless  enemies  the  young  encounter,  few 
live  to  adult  life  from  these  thousands  of  eggs.  Legislation 
which  permits  lobsters  to  be  caught  before  they  are  eight 
inches  long  may  ultimately  be  responsible  for  the  extermi- 
nation of  the  species.  Sensible  laws  and  increased  facilities 
for  hatching  lobsters  in  captivity  and  releasing  them  after  the 
first  critical  stages,  would  do  much  toward  replenishing  the 
lobster  fisheries. 

The  Common  Prawn.  Small  animals  which  live  at  or  near 
the  surface  of  the  water  are,  if  brightly  colored,  so  small  that 
they  are  invisible  ;  if  of  visible  size,  they  incline  toward  trans- 
parency. The  familiar  prawn  (Palccmone'tes  vulga'ris,  frontis- 
piece), found  abundantly  among  seaweeds  near  shore  in  sea 
water  and  also  in  brackish  and  almost  fresh  water,  is  a  good 
example  of  a  pelagic  or  surface-inhabiting  animal  of  consider- 
able size,  which  is  so  nearly  transparent  that  it  may  be  over- 
looked unless  it  moves.  The  prawn,  or,  as  it  is  frequently 
called,  the  shrimp,  is  about  t\vo  inches  long  and  resembles  in 
general  form  the  lobster  or  the  crayfish.  The  body  is,  how- 
ever, more  compressed  (flattened  from  side  to  side),  and  more 
strongly  arched  from  head  to  tail.  The  carapace  is  thin  but 


THE  JOINTED-FOOT  ANIMALS  143 

tough  and  leathery,  and  covered  with  many  reddish-brown 
dots ;  it  is  so  transparent  that  the  stomach  and  intestine  can 
be  seen  clearly  while  the  animal  is  at  rest. 

The  appendages  show  some  interesting  adaptations.  The 
antennas  are  as  long  as  the  body,  very  slender,  and  during 
forward  locomotion  are  constantly  waving  through  the  water. 
One  of  the  antennules  on  either  side  extends  forward,  and  the 
other  backward,  over  the  eye.  At  times,  in  sea-water  aquaria, 
the  recurved  antennule  appears  to  be  clearing  the  surface  of 
the  eye  of  dirt.  The  cheliped  is  only  about  two  thirds  as 
long  as  the  first  walking-leg ;  it  has  the  curious  habit  of 
bending  backward  frequently  at  a  middle  joint  like  a  knee. 
The  first  walking-leg  also  has  a  nipper,  and  is  much  used 
for  grasping  food.  The  remaining  three  appendages  of  the 
thorax  are  about  the  length  of  the  cheliped,  and  em.1  in  a  sin- 
gle point.  When  at  rest  the  prawn  is  usually  found  clinging 
easily  to  the  under  surface  of  seaweeds. 

Crabs.  The  species  represented  in  Fig.  71  (Eupagu'rus 
pollica'ris]  is  called  the  hermit-crab,  probably  because  it  lives 
in  a  "  house  "  by  itself.  The  house  consists  of  the  shell  of  a 
dead  snail  which  may  have  been  washed  to  the  beach,  or  may 
have  rested  on  the  bottom  of  the  bay.  The  hermit-crab  in  its 
early  life  is  pelagic,  but  at  a  certain  stage  of  its  development 
it  sinks  to  the  bottom,  finds  a  snail-shell,  and  backs  into  it ; 
from  that  time  on,  the  general  shape  of  the  body  and  the 
special  modification  of  certain  organs  are  determined  by  the 
form  of  the  snail-shell.  The  abdomen  is  soft,  and  all  the  abdom- 
inal appendages  except  the  terminal  ones  are  misshapen  and 
useless.  The  terminal  appendages  extend  laterally  like  flanges, 
and  prevent  the  body  from  being  drawn  forcibly  from  the 
snail-shell  by  an  enemy.  The  chelipeds  are  abnormally  devel- 
oped and,  besides  being  of  use  in  capturing  prey,  serve  the 
important  function  of  closing  the  aperture  of  the  shell  in 
times  of  danger. 


144 


GENERAL  ZOOLOGY 


Hermit-crabs  live  in  great  abundance  along  gravelly  beaches, 
where  they  are  useful  scavengers  of  dead  animals  in  the  water. 
In  spite  of  the  heavy  houses  which  they  carry,  they  move 
about  with  surprising  facility.  As  suggested  by  one  observer, 
they  are  wary,  cunning,  belligerent,  and  cowardly,  making 
great  pretense  of  fighting,  but  on  the  first  show  of  force  by 
an  opponent  they  withdraw  into  their  shells. 

A  small  shore  species  more  frequently  seen  never  becomes 
as  large  as  Eupagurus  pollicaris,  which  is  a  deep-water  species. 
All  the  species,  however,  when  the  individuals  are  young, 


FIG.  71.  Hermit-Crab  and  Blue  Crab,     x  ± 

choose  small  shells ;  as  they  grow  older  and  larger  after  each 
molt,  the  unused  space  in  the  shell  becomes  less  and  less. 
Naturalists  have  observed  the  action  of  hermit-crabs  that  have 
become  too  large  for  the  shell.  The  animal  searches  about  for 
a  suitable  larger  shell,  and  when  it  finds  one  withdraws  the 
body  from  the  old  shell  and  extends  it  into  the  new. 

The  spider-crab  (Libin'ia  emargina'ta,  frontispiece)  stalks 
slowly  over  the  sea-bottom  in  shallow  and  deep  water  where 
rocks  and  fixed  plants  and  animals  abound.  It  can  neither 
run  nor  swim,  an  inference  which  might  be  drawn  from  the 


THE  JOINTED-FOOT  ANIMALS  145 

slender,  stilt-like  appearance  of  its  legs.  Having  no  means  of 
aggressive  defense,  it  relies  almost  wholly  on  the  fact  that  its 
color  is  very  much  like  its  surroundings.  The  cephalothorax 
is  covered  with  coarse,  hair-like,  flexible  spines,  and  the  gen- 
eral color  is  dull  gray.  Frequently  we  find  on  the  back 
small  seaweeds,  hydroids  (p.  265),  sea-anemones  (p.  252),  and 
even  rock-barnacles  (p.  151),  growing  as  they  would  on  rock. 
This  protective  resemblance  appears  to  be  very  successful 
from  the  point  of  view  of  the  spider-crab,  for  they  are  in  some 
regions  more  abundant  than  any  other  kind  of  crab.  In  some 
parts  of  Long  Island  Sound  the  spider-crabs  are  so  numerous 
that  they  get  into  the  "  lobster-pots  "  set  by  fishermen  and 
crowd  them  so  that  no  inducement  remains  for  the  lobsters 
to  enter,  much  to  the  disgust  of  the  fishermen.  Along  the 
Atlantic  coast  this  species  grows  to  have  chelipeds  which 
extend  over  one  foot  from  tip  to  tip.  The  giant  Japanese 
spider-crab  has  chelipeds  which  extend  over  fifteen  feet  from 
tip  to  tip,  and  has  a  body  correspondingly  large. 

The  edible  crab,  more  frequently  called  by  naturalists  the 
blue  crab  (Callinec'tes  sap'idus,  Fig.  71),  is  characterized  by 
having  sharp  lateral  spines  of  large  size,  and  by  the  last  pair 
of  thoracic  appendages  being  flattened  and  adapted  to  swim- 
ming. The  chelipeds  are  strong  and  fitted  for  cutting ;  the 
succeeding  three  pairs  of  appendages  have  no  nippers,  but 
come  to  a  point. 

As  is  well  known,  the  blue  crab  is  caught  in  large  num- 
bers along  the  Atlantic  and  Gulf  coasts  for  the  markets  in 
the  cities.  The  industry  is  of  considerable  value  commer- 
cially, and  for  that  reason  very  general  attention  has  been 
given  to  the  distribution  and  habits  of  this  crab.  They  are 
caught  most  easily  soon  after  the  molting,  which  takes  place 
in  early  summer,  and  are  then  called  soft-shell  crabs.  It  is 
at  this  time  also  that  they  are  considered  most  valuable  as 
food. 


146 


GENERAL  ZOOLOGY 


The  blue  crab  is  not  confined  to  the  salt  water,  for  it  is 
found  frequently  in  rivers  some  distance  from  bays.  Wherever 
they  are,  they  devour  much  of  the  organic  waste  that  is  carried 
down  to  the  sea.  They  are  therefore  important  as  scavengers. 
The  most  noticeable  feature  in  the  structure  of  the  fiddler- 
crab  (U'ca  pugila'tor,  Fig.  72)  is  the  presence  in  the  males  of 
a  large  cheliped.  Sometimes  it  is  the  right  one  that  is  larger, 

and  sometimes  the  left  one  ;   the 
females  have  their  chelipeds  small 
and    of    equal    size. 
The  name  "  fiddler" 


•<^<     '• 


FIG.  72.    Fiddler-Crab.    Slightly  reduced 


is  supposed 
to  have  been 
derived     from     the 
fancied  resemblance  of 
the  large  cheliped  to  a 
fiddle,  and  of  the  small 
one  to  a  bow. 

Fiddler-crabs  live  in 
the  mud  and  sand  of  salt-marshes  along  the  Atlantic  coast. 
Sometimes  on  the  higher  ground  where  the  sand  is  cleaner 
and  drier,  and  where  vegetation  is  scant,  these  crabs  may  be 
observed  by  the  cautious  visitor,  as  they  glide  quietly  out 
of  their  holes  bearing  pellets  of  sand  and  gravel  under  their 
legs  and  cephalothorax,  to  deposit  the  burden  a  foot  or  more 
away  from  their  holes.  The  species  shown  in  the  picture  has 
been  observed  to  carry  on  this  process  of  excavation  in  the 


THE  JOINTED-FOOT  ANIMALS  147 

brightest  sunshine  and  at  night.  In  feeding  it  seems  to  prefer 
plants,  living  upon  very  small  green  algse  which  grow  on  the 
moist  sand.  The  male  picks  up  these  algse  with  its  small 
cheliped  and  passes  them  to  its  mouth,  or  collects  them  in 
pellets  to  carry  into  its  hole  in  the  same  way  that  it  carries 
pellets  of  sand  out  of  it. 

The  Sow-Bug.  The  sow-bug,  and  a  related  species  called 
the  pill-bug  because  of  its  habit  of  rolling  up  into  a  ball,  are 
found  under  stones,  boards,  logs,  and  in  other  dark,  moist 
places.  They  live  on  vegetable  matter.  The  flattened  con- 
dition of  the  body  reminds  one  of  the  cock- 
roach and  the  cricket,  which  show  the  same 
adjustment  of  the  form  of  the  body  to  the 
necessities  of  their  life.  The  species  repre- 
sented (Fig.  73)  belongs  to  the  genus  Onis'cus. 

The  body  has  twenty  somites,  as  have  the 
crayfish  and  all  the  forms  described  so  far  in 
this  chapter;  five  of  these,  with  one  thoracic 
somite,  are  fused  in  the  head-region ;  seven 
thoracic  somites  are  free-moving,  and  of  the 
seven  abdominal  somites  all  are  free-moving 
except  the  last  two.  A  pair  of  short,  jointed  '  ^w 

antennae  and  a  pair  of  compound  eyes  with- 
out stalks,  i.e.  sessile  eyes  (Lat.  sedere,  to  sit),  are  the  most 
noticeable  prgans  of  the  head.  They  have  a  second  pair  of 
antennae,  which  are  rudimentary.  The  mouth-parts  are  small 
and  adapted  to  feeding  on  plant-food.  The  breathing  organs 
are  gills,  protected  by  flat,  plate-like  structures  on  the  under 
surface  of  the  abdomen.  The  base  of  the  legs  of  the  female 
bears  other  small  plates,  which,  with  the  under  surface  of  the 
body,  form  a  brood-pouch  in  which  the  eggs  are  carried  and 
the  young  developed. 

Caprella.    Probably    one   of   the    strangest   looking    free 
forms  to  be  found  in  the  sea  is  the  little  brown  Caprel'la 


148 


GENERAL  ZOOLOGY 


geomet'rica  (Fig.  74).  Unless  one  should  see  it  represented  in 
its  natural  environment,  or  actually  find  it  there,  the  peculiar 
slender  form  and  the  widely 
separated  groups  of  legs  could 
not  be  explained  on  the 
ground  of  adaptation  to  its 
environment.  The  artist  has 
shown  the  details  of  structure, 
and  also  the  general  resem- 
blance of  the  body  and  ap- 
pendages to  a  portion  of  the 
brown  seaweed.  The  animal 
is  a  little  over  a  centimeter 
long.  The  four  flap-like  ap- 
pendages in  the  middle  regions 
.  are  gills.  Caprella  is 

composed   of   twenty 

somites. 


FIG.  74.    Caprella.     x  2 

Artemia.  The  genus  Arte'mia  is  found  in  brackish  water 
(see  larva,  Fig.  78,  p.  152).  It  is  particularly  interesting  in 
the  light  of  experiments  showing  the  direct  influence  of 
the  environment  on  an  animal  form.  From  1871  to  1874 
the  Russian  naturalist  Schmankewitsch  experimented  with 
Artemia.  In  one  series  of  experiments  he  increased  the 
density  of  the  brackish  water  in  which  they  lived  by  add- 
ing salt ;  in  another  series  he  diluted  the  brackish  water  by 
adding  fresh  water.  After  several  generations  of  Artemia 
had  been  produced  under  these  conditions  it  was  found  that 


THE  JOINTED-FOOT  ANIMALS 


149 


the  individuals  in  the  water  to  which  salt  had  been  added 
were  of  the  form  of  a  species  hitherto  supposed  to  be  dis- 
tinct, and  bearing  a  different  specific  name.  The  individuals 
in  the  water  which  had  been  gradually  diluted  approached 
the  form  of  an  allied  genus.  Thus  a  mere  chang'e  of  the 
amount  of  salt  in  solution  seems  to  have  been  responsible 
for  the  different  forms  assumed  by  the  descendants  of  the 
same  race. 

Cyclops.  Any  fresh-water  pond  will  afford  millions  of  the 
genus  Cy'clops  (Fig.  75),  and  the  sea  contains  species  of  the 
same  genus  in  such  numbers  that  they 
with  allied  genera  form  a  large  part  of  the 
food  of  many  fishes,  and  even  some  species 
of  whales  find  in  them  an  abundant  food- 
supply.  Their  powers  of  reproduction  are 
so  enormous  that  it  has  been  estimated  that 
the  descendants  of  one  Cyclops  may  num- 
ber, in  one  year,  4,500,000,000  individuals. 
Though  microscopic  in  detailed  structure, 
on  close  observation  it  is  easy  to  see  them 
darting  spasmodically  through  the  water 
in  aquaria.  A  single  compound  eye  in  the 
middle  of  the  head  gives  them  their  name, 
in  reference  to  the  race  of  mythical  giants 
of  Sicily.  Two  pairs  of  antennae,  used  in  FlG- 
locomotion,  extend  from  the  front  of  the 
head.  The  legs  are  two-branched  append- 
ages, also  used  in  swimming.  One  pair  of  antennse  and 
the  legs  are  not  shown  in  the  figure.  Two  long  appendages 
extend  from  the  end  of  the  abdomen.  The  body  consists 
of  fifteen  somites,  five  in  each  of  the  three  regions,  head, 
thorax,  and  abdomen.  The  female,  in  the  summer  season,  car- 
ries about  with  her  two  large  brood-sacs  of  eggs  which  exten'd 
diagonally  out  behind. 


5.  Cyclops. 
Much  enlarged. 
(After  Claus) 


150 


GENERAL  ZOOLOGY 


Parasites.    A  large  number  of  different  forms  resembling 
Cyclops    in    many   respects    have   adopted    a    parasitic    life. 
One  of  them  is  shown  in  Fig.  76  (Lernceoc'erci).    They  occur 
on  various  hosts,  but  the  greater  number 
of  them  are  found  on  fishes.    They  live  on 
every  part  of  the  body,  and  in  every  degree 
of  commensalism  and  parasitism.    Some  live 
in  the  alimentary  canal,  or  in  the  gill-region, 
feeding  only  on  the  food  of  the  host ;  some 
temporarily  seek  their  host  for  the  body- 
fluids,    while   others    are  permanent  para- 
sites, external  or  internal.    In  general,  these 
forms  are  spoken  of  as  "  fish-lice."    To  the 
extent  that  they  are  dependent  on  a  host, 
the  normal  external  structure  tends  to  be 
modified  out  of  all  resemblance  to  the  type 
represented  by  Cyclops.    The  somites  lose 
FIG.  76.    Parasitic    their  distinctness,  and  the  form  of  the  body 
Crustacean  Much    ig  altered  b    protuberances  of  various  kinds. 

enlarged.   (After  •>  J 

Von  Nordmann)  The  mouth-parts  become  adapted  as  hold- 
ing and  sucking  organs.  As  the  external 
organs  degenerate,  the  tendency  of  certain  internal  organs  is 
also  to  become  rudimentary.  Some  of  these  parasitic  organ- 
isms are  so  degenerate  in  form  and  structure  that  they  have 
lost  all  appearance  of  being  animals  at  all.  In  many  cases  it 
is  the  female  only  which  is  parasitic,  the  males  leading  a  free 
life  and  showing  the  normal  structure  of  their  race.  As  with 
most  parasites,  immense  numbers  of  eggs  are  produced,  to 
overcome  the  effect  of  the  somewhat  isolated  positions  they 
occupy.  Lernseocera  is  parasitic  on  the  carp,  a  fish.  The 
form  is  considerably  modified,  but  the  egg-sacs  signify  its 
relation  to  Cyclops. 

Barnacles.  Despite  the  great  apparent  difference  between  the 
fixed,  shell-bearing  barnacles  (Fig.  77)  and  the  free-swimming 


THE  JOINTED-FOOT  ANIMALS 


151 


crabs  and  other  forms  discussed  in  this  chapter,  natural- 
ists have  shown  that  they  are  in  reality  closely  allied  both 
in  development  and  in  structure.  The  species  shown  in  the 
accompanying  figure  is  the  rock-barnacle  (Bal'anus  balanoi1- 
des),  the  most  common  barnacle  along  the  North  Atlantic 
coast.  In  some  places  it  literally  incrusts  the  coast-rock 
between  tide  lines  with  its  hard,  sharp-edged  shell,  composed 
of  carbonate  of  lime.  The  shell  is  usually  a  little  over  a 
centimeter  high,  and  narrower  at  the  top  than  at  the  base. 
Related  species  grow  to  be  at  least  four  centimeters  high,  and 


FIG.  77.  Rock-Barnacle.    Reduced 

one  is  found  on  the  back  of  whales.  At  the  top  of  the 
rock-barnacle  are  two  hard,  movable  valves,  meeting  in  a 
median  line,  which,  on  opening,  expose  long,  feather-like 
processes.  These  processes  are,  morphologically,  divisions 
of  the  feet.  The  animal  lies  on  its  dorsal  surface  within  its 
several-valved  shell,  and  by  rapid  movement  of  the  feet  cre- 
ates currents  of  water  which  bring  to  the  mouth  microscopic 
animals  and  plants  as  food.  When  the  feet  are  not  scooping 
in  food  the  valves  are  closed,  forming  a  most  effective  armor 
for  the  parts  beneath. 


152 


GENERAL  ZOOLOGY 


Though  the  barnacle  in  its  adult  condition,  as  just  described, 
has  nothing  to  fear,  in  early  life  the  situation  is  quite  differ- 
ent, for  it  swims  free  at  the  surface  of  the  water  in  the  midst 
of  millions  of  the  young  of  crabs  and  other  animals.  There 
it  is  subject  to  the  attacks  of  animals  which  might  devour  it, 
and  many  young  barnacles  are  undoubtedly  destroyed.  At 
this  time  it  would  not  be  recognized  as  a  barnacle  by  those 
who  have  seen  only  the  adult  form.  It  is  characterized  by 
having  an  unsegmented  body,  a  long  upper  lip,  single  median 
eye,  as  in  Cyclops,  and  three  pairs  of  jointed  locomotor  append- 
ages. This  larval  form  is  called  a  nauplius,  and  resembles 
Fig.  78.  The  barnacle  nauplius  stage  undergoes  further  com- 
plicated changes  before  it  attaches  itself  by  the  head  to  some 
solid  object,  as  a  rock,  pile,  or  ship-bottom,  when  the  swim- 
ming appendages  are  absorbed  and  the  shell  and  feathery 
foot-processes  are  developed. 

Definition  of  Crustacea  (Lat.  crusta,  a  shell).  The  crayfish 
and  the  species  mentioned  thus  far  in  this  chapter  belong 

to  the  class  Crusta'cea.  They 
are  constructed  on  the  plan 
of  a  series  of  body-divisions 
(somites)  seldom  exceeding 
twenty  in  number.  In  gen- 
eral, the  somites  are  bilater- 
ally symmetrical  (uniform  in 
structure  on  either  side  the 
median  line).  Each  somite 
usually  has  a  pair  of  branched, 
jointed  appendages.  As  a 
rule,  two  pairs  of  antennre 

are  present.  A  varying  number  of  thoracic  somites,  in  dif- 
ferent members  of  the  class,  are  fused  to  the  head.  The 
exoskeleton  contains  chitin  and  carbonate  of  lime.  Crustacea 
are  essentially  aquatic  in  their  habits  and,  with  the  exception 


FIG.  78.  Nauplius  Stage  of  Artemia. 
Much  enlarged.     (After  Joly) 


THE  JOINTED-FOOT  ANIMALS  153 

of  the  lowest  forms,  breathe  through  gills.  Nine  tenths  of 
the  class  are  said  to  live  in  the  ocean,  some  in  fresh  water, 
and  relatively  few  on  land. 

As  in  the  insects,  the  hard  exoskeleton  necessitates  fre- 
quent molts  to  provide  for  growth,  and  also,  as  in  that  class, 
growth  is  sometimes  accompanied 
by  marked  metamorphosis  after 
hatching.  The  lower  forms,  such 
as  Cyclops,  the  barnacles,  and  the 
parasitic  Crustacea,  hatch  as  the 
peculiar  nauplius  type  of  larva 
already  mentioned  in  the  descrip- 
tion of  the  rock-barnacle  and  illus- 
trated in  Fig.  78.  FIG.  79.  Zoea  Stage  of  Crab. 

In    the    higher    Crustacea    the         Much  enlarged:   (After 
..  .  Emerton) 

crabs  pass  the  nauplius  stage  in 

the  egg  and  hatch  in  the  zoea  stage  (Fig.  79).  The  lobster 
passes  the  nauplius  and  the  zoea  stage  in  the  egg,  and  hatches 
in  the  my  sis  stage  (Fig.  70).  The  crayfish  passes  all  three 
stages  in  the  egg,  and  hatches  practically  in  the  form  of  the 
adult,  the  young  growing  without  subsequent  metamorpho- 
sis. It  is  important  to  note  that  the  stages  nauplius,  zoea,  and 
mysis,  in  the  development  of  the  higher  Crustacea,  are  practi- 
cally identical  with  the  adult  form  of  certain  other  Crustacea 
which  are  considered  to  be  more  primitive  in  organization. 
The  fact  that  the  lower  type  form  reappears  in  the  develop- 
ment of  the  higher  is  often  cited  as  evidence  in  favor  of  the 
recapitulation  theory  referred  to  in  the  chapter  on  insects. 


THE  TRILOBITES 

Some  of  the  most  abundant  of  the  forms  in  the  earlier 
periods  of  life  on  the  earth  were  the  Tri'lobites  (Pha'cops 
cauda'tus,  Fig.  80),  which  are  now  considered  to  be  closely 


154 


GENERAL  ZOOLOGY 


allied  to  the  Crustacea.  They  are  named  trilobite  from  the 
apparent  division  of  the  body  longitudinally  into  three  parts. 
The  length  of  the  body  varied  from  one 
inch  to  two  feet.  They  are  thought  to 
have  lived  in  shallow  Avaters  along  shores, 
and  through  a  long  period  of  the  earth's 
history  must  have  been  a  most  character- 
istic feature  of  the  fauna  of  the  world. 
Of  the  many  species  of  trilobites  of  which 
we  find  fossils,  not  one  remains  at  the 
present  day. 

THE  HORSESHOE  CRABS:   XIPHOSURA 


FIG.  80.  Trilobite  The  large,   crab-like  animal   shown   in 

(From  Report  of  Geolog-    Fig.  81  is  variously  known  as  the  horse- 

ical  Surve 
Kingdom) 


shoe  crab,  the   king-crab,   the   horsefoot, 


and  by  its  scientific  name,  Lim'ulus  poly- 
phe'mus.  The  first  and  last  common  names  are  derived  from 
the  shape  of  the  cephalothorax.  A  pair  of  simple  eyes  is 
placed  near  the  median  dorsal  line ;  a  pair  of  large  com- 
pound eyes  is  on  the  sides  of  the  cephalothorax.  There  are 
five  pairs  of  legs  on  the  under  surface  of  the  cephalothorax. 
Several  pairs  of  plate-like  gills  are  attached  to  the  under 
surface  of  the  abdomen.  The  body  is  terminated  by  a  long, 
spear-shaped  spine,  —  which  characteristic  gives  the  group 
its  name,  Xiphosu'ra  (Gr.  xiphos,  sword;  oura,  tail). 

Liniulus  is  found  in  sheltered  bays  and  estuaries  along  our 
eastern  coast  from  Maine  to  Florida,  and  on  the  coasts  of 
the  West  Indies  and  Mexico.  In  places  where  it  is  most 
abundant  it  is  caught  with  rakes,  killed,  dried,  and  used 
as  a  fertilizer.  It  is  also  used  for  baiting  eels  and  other  fishes. 
Its  practical  extinction  is  threatened  in  many  places. 

The  illustration  shows  the  horseshoe  crab  almost  buried 
beneath  the  sand  through  which  it  is  plowing  in  search  of 


THE  JOINTED-FOOT  ANIMALS 


155 


worms.  Sometimes  they  plow  a  few  inches  below  the  sur- 
face. The  older  ones,  thirty  to  forty  centimeters  in  length 
(twelve  to  sixteen  inches),  burrow  in  deeper  water;  small 
ones  may  often  be  seen  on  sand-flats  where  the  water  is 
only  a  few  inches  deep.  At  the  time  of  high  tides  in  May, 
June,  and  July,  the  mature  males  and  females,  the  latter 
always  the  larger,  leave  the  water  and  make  their  way  up 
the  sandy  shore  to  a  point  just  below  high-water  mark.  The 
female  digs  a  hole  in  the  sand,  deposits  her  eggs,  and  the 
male  follows  and  deposits  the  "  milt,"  or  spermatozoa,  over 
the  eggs.  Both  animals  then  return  to  the  deeper  water, 
and  the  retreating  tide  covers  the  eggs  with  sand.  The  young 


Of, 


FIG.  81.  Horseshoe  Crab 


hatch  in  about  four  or  five  weeks,  and  make  their  way  into 
shallow  water.  When  first  hatched  they  resemble  young 
trilobites  in  form. 

The  horseshoe  crab  is  a  peculiar  type.  It  shows  many 
points  of  similarity  to  both  crustaceans  and  arachnids,  par- 
ticularly the  scorpions,  and  it  may  be  that  the  latter  have 
descended  from  these  aquatic  forms,  which  are  an  extremely 
ancient  stock.  Some  of  the  fossil  allies  of  the  horseshoe  crab 
grew  to  be  five  or  six  feet  long. 


156  GENERAL  ZOOLOGY 

DEFINITION  OF  ARTHROPODA 

The  animals  described  so  far  in  this  book  belong  to  the 
phylum  (see  p.  97)  Arthrop'oda  (Gr.  arthron,  joint;  pous  (pod), 
foot).  All  but  a  very  few  members  of  this  phylum  are  in- 
cluded in  the  four  classes,  Hexapoda,  Arachnid  a,  Myriapoda, 
and  Crustacea. 

The  body  of  an  arthropod  is  made  up  of  bilaterally  sym- 
metrical somites  arranged  in  a  linear  series.  There  is  always 
a  head  composed  of  from  four  to  six  fused  or  united  somites. 
The  somites  of  the  remainder  of  the  body  are  grouped  into 
one  region,  the  trunk  (Myriapoda) ;  or  into  two  regions,  thorax 
and  abdomen  (Hexapoda,  some  Crustacea).  The  head  is  some- 
times fused  with  the  thorax,  the  abdomen  being  a  distinct 
region  (Arachnida,  some  Crustacea).  Appendages,  wherever 
present,  are  jointed  or  segmented,  and  occur  as  single  pairs 
on  somites.  The  somites  and  appendages  are  covered  with  a 
chitinous  exoskeleton ;  in  some  members  of  the  phylum  the 
exoskeleton  is  very  hard,  and  filled  with  carbonate  of  lime. 

The  digestive  tract  extends  nearly  straight  through  the 
body  from  the  anterior  end  to  the  posterior  end.  The  blood, 
which  is  colorless,  is  carried  through  the  body  in  a  partially 
complete  system  of  vessels  with  a  tubular,  or  heart-like,  pump- 
ing organ  in  the  dorsal  region  of  the  body-cavity. 

Respiration  takes  place  through  gills  (Crustacea),  lung-like 
sacs  (Arachnida),  or  through  an  internal  network  of  tubes 
(tracheae)  opening  in  two  lateral  series  on  the  exterior  of  the 
body  (Myriapoda,  Hexapoda,  and  some  Arachnida). 

The  nervous  system  generally  consists-  of  a  "brain,"  dorsal 
to  the  gullet,  two  connectives  passing  one  on  either  side  of 
the  gullet,  and  uniting  below  to  form  a  ganglion,  from  which 
a  double  nerve-cord  extends  along  the  ventral  body-wall  to 
the  posterior  end.  Sense-organs  characteristic  of  the  phylum 
are  segmented  tactile  organs,  and  simple  and  compound  eyes. 


CHAPTER  XIV 
THE  CLAM  AND  OTHER  BIVALVES:    PELECYPODA 

And  I  then  engaged  myself,  with  the  other  merchants,  in  a  pearl  fishery 
in  which  I  employed  many  divers  on  my  own  account. 

SINDBAD  THE  SAILOR,  Arabian  Nights. 

THE  LONG-NECK  CLAM 

Habitat  and  Distribution.  The  animal  which  is  described 
first  in  this  chapter  is  commonly  known  as  the  long-neck 
clam  or  the  soft-shell  clam.  It  is  more  accurately  designated 
by  its  scientific  name,  My 'a  arena' ria  (Fig.  82).  As  the  spe- 
cific name  implies,  the  animal  lives  in  the  sand.  It  is  found 
in  great  abundance  along  our  Atlantic  coast,  even  as  far  north 
as  the  Arctic  regions. 

External  Structure.  The  shell  of  the  clam  has  the  same  gen- 
eral use  as  the  carapace  of  the  crayfish.  In  both  animals  these 
hard  external  parts  protect  the  organs  within  from  injury,  and 
also  afford  surface  for  the  attachment  of  muscles.  The  clam's 
shell,  however,  is  never  molted.  It  grows  continuously  from 
the  time  it  begins  existence,  at  the  little  rounded  prominence 
called  the  umbo  (pi.,  umbones),  or  beak  (Fig.  82,  l). 

Any  one  who  has  examined  a  dry  shell  of  this  kind  can 
tell  which  is  the  youngest  portion  of  the  shell.  Probably  he 
will  observe  at  the  same  time  the  little  spoon-shaped  piece 
extending  horizontally  inward  from  one  of  the  valves  of  the 
shell.  This  projection  is  always  on  the  left  valve.  It  meets 
a  brown,  rubber-like  pad  beneath  the  umbo  of  the  right  valve, 
and  is  joined  with  it.  As  long  as  the  two  valves  hold  together 
at  this  point,  the  pad,  which  is  called  the  hinge-ligament,  has 
a  tendency  to  separate  the  valves  at  an  acute  angle.  In  life 

157 


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158 


THE  CLAM  AND  OTHER  BIVALVES 


159 


two  thick,  short  muscles  (Fig.  82,  2,3;  Fig.  83,  2  a)  extend 
across  from  valve  to  valve,  and  resist  the  spreading  action 
of  the  hinge-ligament. 

The  Mantle  and  the  Mantle-Cavity.  When  the  valves  are 
shut  they  inclose  a  considerable  space  besides  the  body 
proper.  Fig.  82 
represents  the 
most  important 
organs  as  they 
might  lie  in  the 
hollow  of  the 
right  valve.  Fit- 
ting close  to  the 
inner  surface 
of  the  valves  is 
the  mantle  (Fig. 
82,4).  Except  at 
the  edge,  where 
the  mantle- folds 
(halves)  unite,  the 
mantle  is  quite 
thin;  its  chief 
use  is  to  secrete 
the  calcareous 
substance  of 
which  the  shell 

is  composed.  The  shell  is  deposited  in  three  layers  (Fig.  83, 
3,  4,  5),  —  the  outer  layer  called  the  periostracum,  the  middle 
layer  called  the  prismatic  layer,  and  the  inner  layer  called  the 
nacreous  or  pearly  layer.  After  the  shell  is  formed  at  the  edge 
the  thin  part  of  the  mantle-folds  continues  to  deposit  the 
nacreous  layer,  which  is  sometimes  called  mother-of-pearl. 

The  mantle-folds  inclose  a  mantle- cavity.    An  opening  at  the 
anterior  end  of  the  mantle-cavity  allows  the  foot  (Fig.  82,  5), 


FIG.  83.   Mechanism  for  opening 
Mussel-Shell 


A,  valves  of  mussel  closed;  B,  valves  of  mussel  open: 
1,  2,  hinge-ligament;  2a,  adductor  muscle  contracted; 
2b,  adductor  muscle  relaxed ;  3,  outer  layer  of  shell ; 
4,  middle  layer  of  shell;  5,  inner  (mother-of-pearl) 
layer 

(From  Lang's  Lehrbuch) 


160  GENERAL  ZOOLOGY 

the  single  locomotor  organ,  to  be  extended  to  the  outside. 
At  the  posterior  end  of  the  mantle-cavity  is  situated  the 
double-tubed  siphon  (Fig.  82,  6).  Only  the  lower  tube  of 
the  siphon  is  connected  directly  with  the  mantle-cavity. 
This  siphon  enables  Mya  to  lie  buried,  anterior  end  down, 
in  the  mud  and  sand,  still  maintaining  communication  with 
the  food-laden  and  air-laden  water  above.  In  large  specimens 
of  this  clam  the  siphon  is  over  25  cm.  (10  in.)  long. 

The  Digestive  System.  The  ventral  opening  of  the  siphon 
(Fig.  82,  7)  is  surrounded  by  many  short  tentacles  which 
guard  the  passage.  An  ingoing  current  is  created  in  the 
water  by  cilia  on  the  gills.  Ordinarily  only  microscopic  food 
passes  through  this  incurrent  opening  of  the  siphon.  In  the 
mantle-cavity  the  particles  of  food  are  carried  forward  over 
the  gills  and  along  the  mantle  till  they  come  within  range 
of  the  waving  palps,  or  mouth-appendages  (Fig.  82,  9). 

The  mouth-opening  (Fig.  82,  10)  is  situated  between  the 
four  palps,  and  is  very  small.  It  has  no  organs  of  any  kind 
for  seizing  or  chewing  food ;  none  are  needed.  The  food 
once  swallowed  passes  through  the  short  oesophagus  to  the 
stomach  (Fig.  82,  11).  Surrounding  the  stomach  is  the  large, 
paired  digestive  gland  (Fig.  82,  12).  which  secretes  the  diges- 
tive fluid.  Situated  in  the  end  of  the  stomach,  and  in  the 
anterior  end  of  the  intestine,  we  find,  in  Mya  arenaria,  and 
in  many  species  related  to  it,  an  organ  called  the  crystalline 
style  (Fig.  82,  14).  In  Mya  this  structure  is  three  or  four 
inches  long.  It  is  soft  and  clear  like  thick,  colorless  jelly, 
and  lies  in  a  long,  thin-walled  sac  opening  into  the  stomach. 

Many  theories  have  been  advanced  to  account  for  the  exist- 
ence of  the  crystalline  style.  Recently  (1901)  the  nature  of 
the  structure  was  investigated  by  Professor  Mitra,  a  physio- 
logical chemist  living  in  Calcutta,  India.  He  has  published 
an  account  based  on  experimental  evidence,  which  appears  to 
be  satisfactory.  His  conclusion  is  that  the  crystalline  style 


THE   CLAM  AND   OTHER   BIVALVES  161 

of  a  certain  fresh-water  mussel  (An'odon)  is  the  condensed 
secretion  of  the  digestive  gland ;  its  function  is  to  convert 
starch  into  sugar.  After  a  period  of  feeding  and  subsequent 
digestion  the  style  disappears  and  is  later  formed  anew. 

The  intestine  (Fig.  82,  13)  coils  and  twists  in  many  planes 
from  the  posterior  end  of  the  stomach  to  the  point  where  it 
penetrates  the  heart.  The  penetration  of  the  heart  by  the 
intestine  is  of  common  occurrence  in  the  class  to  which  Mya 
belongs,  but  it  occurs  in  no  other  class  of  animals.  The  part 
of  the  alimentary  canal  from  the  heart  to  the  anus  (Fig.  82, 16) 
is  called  the  rectum  (Fig.  82,  15).  The  rectum  is  inclosed 
in  a  large,  spindle-shaped  organ  (Fig.  82,  17)  of  unassigned 
name  and  unknown  function. 

The  Circulatory,  Respiratory,  and  Excretory  Systems. 
When  the  food  is  absorbed  by  the  wall  of  the  intestine  it 
passes  into  small  blood-spaces  filled  with  colorless  blood. 
The  blood  with  the  contained  food  then  passes  into  the 
open  ends  of  small  blood-vessels.  These  blood-vessels  lead 
(in  certain  near  relatives  of  Mya  which  have  been  studied 
more  fully)  to  a  large  blood-space  below  the  pericardium 
(Fig.  82,  18),  the  sac  which  incloses  the  heart.  From  the 
blood-space  (not  shown  in  the  figure)  blood  passes  by  vessels 
to  the  nephridia  (kidneys).  The  nephridia  in  Mya  arenaria 
lie  one  on  either  side  near  the  heart.  The  anterior  end  of 
the  left  nephridium  is  indicated  at  Fig.  82,  19.  The  rest  of 
the  organ  could  not  be  shown  in  the  drawing. 

The  nephridia  are  spongy,  brownish  organs  of  great  com- 
plexity. They  are  sometimes  referred  to  under  the  name 
"organs  ofBojanus."  The  old-time  anatomist,  Bojanus,  dis- 
covered the  structures,,  but  he  made  a  most  natural  mistake 
in  thinking  that  they  were  the  lungs  of  the  animal,  since  they 
look  like  lungs  and  lie  very  near  the  heart.  Other  anatomists 
gave  the  name  "  organs  of  Bojanus,"  and  later  investigators 
found  that  the  organs  were  alike  in  structure  and  in  function 


162  GENERAL  ZOOLOGY 

to  the  nephridia  of  simpler  animals.  Each  nephridium  of  the 
clam  opens  by  one  end  into  the  pericardium.  The  other  end 
of  each  nephridium  opens  into  the  mantle-cavity  just  posterior 
to  the  digestive  gland. 

As  the  blood-vessels  in  the  nephridia  divide  into  capilla- 
ries, the  nitrogenous  waste  of  the  body  (uric  acid)  passes  into 
the  nephridial  tube  and  is  carried  out  into  the  mantle-cavity. 
The  small  blood-vessels,  reuniting  into  large  vessels,  convey 
the  partially  purified  blood  into  a  vessel  that  runs  along  the 
line  of  attachment  of -the  gills. 

There  are  four  of  these  gills  and  they  hang  like  double 
curtains  along  the  right  and  left  sides  of  the  body  (Fig.  82,  20). 
The  oxygen  coming  into  the  mantle-cavity  with  the  water, 
through  the  incurrent  tube  of  the  siphon,  passes  over  the 
floating  gills.  They  are  thin  and  soft,  arid  are  thus  adapted 
for  the  ready  passage  of  oxygen  to  the  blood-vessels  inside. 

In  the  blood  the  oxygen  combines  with  Immocyanin,  a 
substance  analogous  to  hemoglobin  (see  p.  203).  At  the  same 
time  the  waste  carbon  dioxide  in  the  blood  is  given  off  to 
the  water  in  the  mantle-cavity.  The  mantle-folds,  as  well 
as  the  gills,  take  part  in  respiration.  It  is  possible  for  them 
to  do  so  because  of  their  rich  supply  of  superficial  blood- 
vessels. 

Returning  from  the  gills  and  the  mantle,  the  blood  freed 
of  carbon  dioxide  is  carried  to  the  right  (Fig.  82,  21)  and  left 
auricles  of  the  heart.  These  thin-walled,  sac-like  reservoirs 
force  the  blood  into  the  ventricle  (Fig.  82,  22)  of  the  heart 
through  valve-guarded  openings  on  either  side  (Fig.  82,  23). 
The  heart  contracts  and  forces  the  blood  both  forward  and 
backward  through  arteries.  The  anterior  artery  lies  above 
the  intestine  (Fig.  82,  24),  and  the  posterior  artery  lies  below 
the  rectum  (Fig.  82,  25).  Both  arteries  branch  into  smaller 
arteries  in  all  parts  of  the  body.  The  blood  flows  from  the 
open  ends  of  the  smallest  arteries  into  blood-spaces,  from 


THE  CLAM  AND  OTHER  BIVALVES  163 

which  it  is  once  more  collected  and  carried  to  the  purifying 
organs  in  the  manner  already  described. 

The  Excurrent  Tube.  Besides  the  rows  of  cilia  which  carry 
food  from  the  region  of  the  in  current  tube  to  the  mouth, 
there  are  rows  of  cilia  on  the  body  and  along  the  mid- 
ventral  line  of  the  mantle,  and  it  is  known  that  these  cilia 
wave  toward  the  incurrent  tube.  Food  that  has  been  rejected, 
or  waste  that  has  accumulated,  may  be  carried  by  the  out- 
waving  cilia  to  the  base  of  the  incurrent  tube.  By  muscular 
contraction  of  the  siphon  at  its  base  these  substances  may  be 
expelled  through  the  tube.  The  dorsal  tube  of  the  siphon, 
however,  is  the  customary  path  of  exit  for  substances  that  are 
not  used  by  the  organism.  All  the  undigested  substances  that 
pass  through  the  intestine  must  leave  the  animal  by  the  dor- 
sal tube.  In  addition,  it  is  likely  that  wastes  from  the  neph- 
ridia,  and  from  the  gills  and  mantle,  may  pass  from  the 
mantle-cavity  through  a  slit-like  opening  (Fig.  82,  26)  at  the 
base  of  the  gills,  and  be  carried  out  with  the  unused  materials. 

The  Nervous  System.  Lying  on  the  right  and  left  sides  of 
the  oesophagus,  just  posterior  to  the  mouth,  is  a  pair  of  cerebro- 
pleural  ganglia  (Fig.  82,  27).  They  are  joined  by  a  cerebral 
commissure  running  over  the  oesophagus.  As  the  name  of 
the  ganglia  implies,  there  are  two  ganglia  joined  in  each  nerve- 
mass.  One  pair  controls  the  "  head  "  region  ;  the  other  pair 
controls  the  sides  of  the  body  near  by.  The  cerebro-pleural 
ganglia  are  joined  to  the  pedal  (foot)  ganglion  (Fig.  82,  28) 
by  two  connectives,  one  on  either  side  (Fig.  82,  29).  The 
pedal  ganglion  controls  the  movements  of  the  foot.  The  vis- 
ceral ganglion  (Fig.  82,  30)  is  joined  to  the  cerebro-pleural 
ganglia  by  a  pair  of  cerebro-visceral  connectives  (Fig.  82,  31). 
The  visceral  ganglion  controls  the  organs  in  the  posterior 
region  of  the  body. 

The  Reproductive  System.  The  pair  of  large  glands  (Fig. 
82,  32),  which  in  male  and  female  clams  contains  spermatozoa 


164 


GENERAL  ZOOLOGY 


3--- 


or  the  eggs,  lies  in  the  midst  of  the  coils  of  the  intestine. 
Each  gland  has  a  short,  slender  tube,  with  an  external  opening 
(not  shown)  near  the  opening  of  the  nephridium,  just  below 
the  attachment  of  the  gills. 

Development.  The  very  early  history  of  the  }roung  Mya 
arenaria  has  not  been  studied.  We  know,  however,  that 

after   a   short    period   of 
development  and  growth 
young    long-neck    clams 
I  swim  about  on  the  sur- 

face of  the  water.  Soon 
after  the  appearance  of  their  shell 
they  sink  to  the  bottom.  If  they  are 
fortunate  enough  to  fall  near  the 
shore-line,  they  anchor  themselves 
to  a  seaweed,  or  to  a  pebble,  by  a 
tough,  gelatinous  thread  (Fig.  84,  3) 
which  is  secreted  by  a  gland  at  the 
5ck  base  of  the  foot  (Fig.  84,  l).  This 
thread  is  called  the  byssus.  In  cer- 
tain mussels  found  in  the  sea  the 
byssus  is  a  permanent  and  very  com- 
plicated organ  of  the  adult,  but  in  Mya  arenaria  it  disappears 
when  the  clam  is  about  5  millimeters  (l-  inch)  long.  At  that 
time  the  animal  burrows  into  the  mud  and  sand,  where  it 
usually  remains  permanently. 

Relation  to  Environment.  The  adult  Mya  arenaria  lives 
in  soft  mud  and  sand  between  high-tide  line  and  a  few  feet 
beyond  low-tide  line.  The  reason  the -clam  lives  in  that 
situation  is  because  food  is  most  abundant  there.  Lying 
almost  helpless  in  its  mold  of  mud,  the  long-neck  clam  is 
rendered  in  a  measure  independent  of  conditions  outside,  as 
long  as  the  currents  of  water  carry  the  bountiful  supplies  of 
food  over  its  burrow. 


Clam.   (After  J.  L.  Kellogg) 

1,  foot;  2,  siphon;    3,  byssus- 
thread;  4,  pebbles 


THE   CLAM  AND   OTHER   BIVALVES  165 

If  a  young  clam  escapes  the  danger  of  being  carried  out 
to  sea  during  its  pelagic  life,  it  is  safe  for  a  while  when,  on 
sinking  to  the  bottom,  it  anchors  to  some  fixed  or  heavy  ob- 
ject with  its  byssus-thread.  There  it  encounters  dangers  from 
food-hunting  fish.  Still  more  dangerous  are  the  storms  that 
carry  waves  of  water  far  up  the  beach  and  leave  to  destruction 
many  kinds  of  animals  that  happen  to  be  borne  along.  At 
the  same  time  countless  young  of  the  clams  that  escape  being 
carried  out  must  be  smothered  by  the  shifting  sand  and  mud. 

As  the  adult  stage  approaches  the  dangers  of  existence 
become  less  and  less,  until  man  himself  interferes  with  the 
natural  balance  of  chances  in  the  clam's  life.  In  certain 
parts  of  the  Atlantic  coast,  especially  in  the  vicinity  of  large 
cities,  the  species  is  fast  being  exterminated.  Although  the 
clam  is  not  as  highly  esteemed  as  an  article  of  human  food 
as  its  relative  the  oyster,  it  is  nevertheless  of  great  value. 
Officers  of  the  Bureau  of  Fisheries  have  considered  the  mat- 
ter of  restricting  the  digging  of  clams,  and  also  various  means 
of  tiding  the  young  over  the  danger-points  in  their  lives. 

THE  AMERICAN  OYSTER 

Habitat  and  Distribution.  The  American  oyster  (Os'trea 
virginia'na,  Fig.  85)  is  found  in  shallow  to  deep  water  along 
the  Atlantic  coast  from  the  Gulf  of  Mexico  to  Massachu- 
setts Bay.  As  the  artist  has  shown  in  the  picture,  the  animal 
lies  attached  to  the  bottom,  frequently  to  another  oyster-shell. 
Although  many  oysters  may  live  thus  fastened  to  each  other, 
there  is  no  organic  connection  between  them.  They  some- 
times form  clumps  so  large  and  heavy  that  the  basal  ones 
sink  into  the  mud  and  die.  The  valves  of  the  living  ones 
extend  outward  at  any  angle.  When  oysters  are  not  crowded 
iri  the  "  bed,"  the  usual  method  of  living  is  the  one  shown 
in  the  illustration.  There  the  valves  extend  horizontally, 


166 


GENERAL  ZOOLOGY 


and  we  can  distinguish  an  upper  and  a  lower  valve.  The 
lower  valve  is  always  much  larger  and  deeper  than  the  upper 
one.  The  lower  one  is  the  left  valve. 

Comparison  with  the  Clam.  The  internal  organs  of  Ostrea 
virginiana  and  Mya  arenaria  are  very  much  alike.  The  large, 
dark-brown  digestive  gland,  the  coiled  intestine,  the  three- 
chambered  heart,  and  the  reproductive  glands  have  a  common 
plan  in  the  two  species.  A  noticeable  difference  is  the  entire 
absence  of  a  foot  in  the  oyster.  Applying  the  principle  of 
adaptation,  we  can  readily  explain  the  absence  of  that  organ. 
The  two  animals  are  different  also  in  the  number  of  adduc- 
tor muscles.  In  the  clam  there  are  two  ;  in  the  oyster  only 
one.  The  muscle-scar  on  the  inner  surface  of  the  valves  of 
an  oyster  is  a  dark  blotch.  As  the  oyster  grows  from  season 
to  season  the  location  of  the  shell-closing  muscle  changes 


FIG.  85.  Group  of  Living  Oysters.    Reduced 

to  meet  the  necessity  of  performing  its  function  most  advan- 
tageously. In  a  lot  of  a  dozen  oyster- valves  the  observer 
may  find  several  which  indicate  this  change.  In  some  valves 
all  trace  of  the  change  is  concealed  by  the  thick  layer  of 
mother-of-pearl  laid  down  by  the  mantle  after  the  muscle 
altered  its  position. 


THE   CLAM  AND   OTHER  BIVALVES 


167 


FIG.  86.  Oyster  Larva.  Much 
enlarged.  (After  Mcebius) 

1,  mouth;  2,  stomach;  3,  aims; 
4,  shell ;  5,  adductor  muscle ; 
0,  circle  of  cilia 


Development.  In  the  months  of  May,  June,  and  July,  in 
the  latitude  of  Baltimore,  the  male  and  female  oysters  send 
out  into  the  water  their  spermatozoa  and  their  eggs.  Pro- 
fessor Brooks,  of  Johns  Hopkins 
University,  estimates  the  number 
of  eggs  which  a  female  oyster 
may  yield  in  one  season  to  be  at 
least  nine  million.  "The  number 
of  male  cells,"  he  says,  "  is  great 
beyond  all  powers  of  expression." 
Of  course  we  should  expect  that 
in  spite  of  the  countless  sperma- 
tozoa, many  eggs  would  never  be 
fertilized  at  all,  on  account  of 
their  being  carried  away  by  un- 
favorable currents.  Eggs  that  are 
not  carried  away  fall  to  the  bot- 
tom naturally.  Those  eggs  which  are  fertilized  swim  to 
the  surface  as  larvae  after  a  few  hours'  development.  There 
surface-fish  may,  as  Professor  Brooks  suggests,  "  gulp  down 
in  a  few  seconds  oysters  equal  in  number  to  the  population 
of  Baltimore." 

Within  one  to  six  days  after  fertilization  the  oyster  "  fry  " 
(swimming  larvae,  Fig.  86)  sink  to  the  bottom  again  and  affix 
themselves  by  the  margin  of  the  left  mantle-fold  to  whatever 
solid  object  they  happen  to  touch.  At  this  time  they  are 
about  .3  mm.  (^  in.)  long.  For  a  few  weeks  after  beginning 
their  stationary  life  they  are  liable  to  be  crunched  to  death 
by  voracious  crabs,  —  among  others,  the  blue  crab  (Fig.  71). 

Economic  Importance.  The  largest  and  most  important 
"  oyster-farms "  along  our  coast  are  in  Chesapeake  Bay. 
There  and  elsewhere  the  beds  have  been  surveyed  and  leased 
under  laws  of  the  states.  So  vast  is  the  oyster-fishing  industry 
in  this  country  that  millions  of  dollars  are  paid  annually  by 


168  GENERAL  ZOOLOGY 

the  markets  of  the  large  cities  for  these  "  esculent  bivalves." 
On  the  coasts  of  Holland,  Belgium,  and  France  far  greater 
care  is  taken  of  their  species  (Ostrea  ed'ulis)  than  we  take 
of  ours ;  but  the  natural  conditions  here  are  superior  to  the 
natural  conditions  there. 

Relation  to  Environment.  According  to  the  investigations 
of  Professor  Brooks,  Professor  Ryder,  and  others,  oysters  are 
to  be  found  most  abundantly  in  the  quiet,  semistagnant  water 
of  shallow  inlets.  Into  such  inlets  slowly  flowing  creeks 
enter,  giving  to  the  water  of  the  inlet  a  brackish  quality. 
When  food  consisting  of  microscopic  plants  and  animals  is 
carried  to  the  oyster  by  the  natural  currents  in  the  water,  it 
may  enter  at  any  point  between  the  separate  folds  of  the 
mantle.  Cilia  on  the  inner  surface  of  the  mantle-folds,  and 
on  the  four  gills,  sweep  the  minute  organisms  forward  to  the 
mouth,  which  lies  near  the  hinge.  The  four  palps  aid  in  the 
process.  In  brackish  water  the  most  important  food-organism 
of  the  oyster  multiplies  in  vast  invisible  hordes.  These 
organisms  are  plants  called  diatoms.  Diatoms  live  in  the 
soft  mud  at  the  bottom,  and  are  carried  by  the  water-currents 
within  range  of  the  cilia  in  the  oyster's  mantle-folds. 

In  times  of  storm  the  home  of  the  oysters'  food  may  become 
a  source  of  great  danger  to  them.  Once  covered  with  mud  or 
with  shifting  sand,  the  life  of  a  bed  of  oysters  is  at  an  end. 
At  the  mouths  of  rapidly  flowing  rivers  no  oysters  are  to  be 
found,  chiefly  because  the  silt  (fine  sediment)  and  the  debris 
of  decaying  plants  are  unfavorable  to  the  growth  of  the  animal. 

Aside  from  the  physical  agencies  which  are  favorable  or  un- 
favorable to  oysters,  there  are  many  animals  which  come  into 
definite  and  usually  unfavorable  relations  to  them.  Only  one 
of  these  animals,  so  far  as  known,  is  anything  but  harmful 
to  the  oyster.  That  one  is  a  little  crab,  about  13  millimeters 
(^  inch)  wide,  which  spends  its  life  in  the  mantle-cavity  of 
its  messmate.  Trie  greatest  enemy  of  the  adult  oyster  is  the 


THE   CLAM  AND   OTHER   BIVALVES  169 

starfish  (Fig.  118).  There  are  various  boring-snails,  which 
make  round  holes  through  one  of  the  valves  with  their  rasp- 
ing-tongues and  draw  out  what  they  need  of  the  soft  parts 
(compare  Fig.  99).  Another  enemy  is  the  boring-sponge, 
which,  as  it  grows,  makes  holes  in  the  valves  by  a  secretion 
which  it  produces.  Like  most  other  animals,  the  oyster  has 
its  parasites.  With  all  these  facts  before  us,  the  statement 
of  Professor  Mobius  regarding  the  European  oyster,  that 
each  oyster  when  born  has  -  -  of  a  chance  to  survive 

J  1145000 

and  reach  adult  age,  seems  well  within  reason. 

THE  SCALLOP 

Habitat  and  Distribution.  Of  all  the  "shell-fish"  that  in- 
habit the  shallow  waters  of  the  Atlantic  coast  of  our  country, 
none  is  more  beautiful  in  color  or  in  line  than  the  common 
scallop,  Pec' ten  irra'dians  (Fig.  87).  Scallops  are  abundant 
among  the  eel-grass  of  shallow  bays  and  inlets  from  the  Gulf 
of  Mexico  to  Massachusetts  Bay.  Above  the  latter  region 
the  waters  are  made  colder  by  the  Arctic  currents.  Pecten 
irradians  and  many  other  species  of  sea-animals  do  not  live 
north  of  Cape  Cod.  There  are,  however,  many  species  of  ani- 
mals that  flourish  best  in  the  cold  waters  of  Maine  and  the 
maritime  provinces  of  Canada. 

Relation  to  Environment.  The  very  young  scallop  holds  to 
some  fixed  object  after  the  manner  of  a  young  soft-shell  clam 
(Fig.  84).  The  adult  scallop  has  no  byssus,  and  only  the 
rudiment  of  a  foot.  The  scallop  in  the  foreground  of  the 
picture  is  in  what  we  might  call  the  attitude  of  rest.  It  has 
released  its  single  adductor  muscle,  which,  we  may  say  in 
passing,  is  the  only  part  of  the  animal  sold  for  food.  The 
mantle-folds  of  the  resting  scallop  expand,  showing  at  the 
margin  slender  tentacles  and  a  variable  number  of  delicate 
cobalt-blue  eyes.  If  a  person  causes  a  shadow  to  pass  over 


170 


GENERAL  ZOOLOGY 


the  margin  of  the  mantle,  the  mantle  is  withdrawn  and  some- 
times the  valves  are  closed.  The  same  experiment  may  be 
tried  on  the  oyster  with  similar  results,  although  the  oyster 
has  no  eyes  at  all.  Invisible  sense-organs  in  that  animal 
respond  to  the  stimulus  of  light. 

While  feeding  and  breathing,  the  tentacles  of  the  scallop 
aid  the  cilia  of  the  mantle,  gills,  and  palps  in  conveying  food 
to  the  mouth.     At  such  times  the  spores  of  various  seaweeds 
and    the   young    of   certain   snails    (Crepid'ula,   on 
scallop  in  foreground,  Fig.  87)  may  find  a  surface 
of  attachment  on  one  of  the  valves.     These 
organisms  have  an  advantage  over  station- 
ary individuals  of  the  same  species, 
in  being  attached  to  a  movable 
support,   for,   when  the   scallop 
swims  about,  the  messmates  are 
carried    to    new    and    possibly 
better  stores  of  food. 

If  one  were  to  reason  from 
the  general  appearance  of  the 
scallop  which  part  should  go  for- 
ward when  the  animal  swims,  it 
is  verv  likely  that  the  conclusion 


FIG.  87.    Group  of  Living  Scallops. 


THE  CLAM  AND  OTHER  BIVALVES  171 

would  be  different  from  the  actual  performance.  The  attitude 
of  a  swimming  scallop  is  portrayed  in  the  upper  left-hand  part 
of  the  illustration.  In  the  act  of  swimming  the  valves  open 
and  close  quickly,  by  the  alternate  action  of  the  hinge-liga- 
ment and  the  large  adductor  muscle.  On  closing,  the  valves 
catch  a  quantity  of  water  between  the  mantle-folds.  The 
water  escapes  under  pressure  from  within,  through  a  round 
opening  at  either  end  of  the  straight  flange  of  the  hinge. 
The  resulting  action  of  these  jets  of  water  backward,  against 
the  body  of  water  outside,  is  to  force  the  larger  and  broader 
end  of  the  animal  forward.  Locomotion  is  not  in  a  direct  line, 
but  over  a  zigzag  course.  When  the  scallop  ceases  swimming 
it  immediately  falls  to  the  bottom.  The  animal  is  not  what 
one  would  call  a  skillful  swimmer,  although  its  movements 
are  very  interesting  to  observe. 

THE  FRESH-WATER  MUSSEL 

Habitat  and  Distribution.  In  fresh  waters  generally,  wher- 
ever sufficient  carbonate  of  lime  is  carried  in  solution,  one 
may  find  mussels  living  nearly  covered  in  sand  and  mud. 
The  species  represented  in  Fig.  88,  U'nio  complana'ta,  is 
distributed  in  the  rivers  and  brooks  of  the  entire  country. 

Comparison  with  Other  Forms.  The  valves  of  the  mussel  are 
equal,  like  those  of  the  clam  and  the  scallop.  The  valves  of 
the  .fresh- water  species  are  held  together  by  a  hinge-ligament, 
aided  by  two  pearl-covered  ridges  running  parallel  and  fitting 
into  grooves.  The  mantle-folds  are  not  united,  as  they  are  in 
the  clam.  At  two  adjoining  places  in  the  posterior  region  the 
rim  of  the  mantle-folds  is  fringed  with  short  tentacles.  Dorsal 
and  ventral  tubes  are  formed  by  the  meeting  of  opposite  edges 
at  the  places  where  the  tentacles  occur.  Food  and  oxygen  are 
carried  in  by  the  ventral  tube,  and  undigested  substances  are 
carried  out  by  the  dorsal  tube.  We  may  speak  of  the  siphon 


172 


GENERAL   ZOOLOGY 


of  the  mussel,  but  as  a  matter  of  strict  accuracy  the  mussel 
does  not  have  a  siphon,  in  the  sense  that  the  clam  possesses 
one.  The  foot  of  the  mussel  is  large  and  muscular.  It 
enables  the  animal  to  plow  its  way  through  mud  or  even 
through  heavy  gravel.  The  gills  and  the  palps  are  practically 
identical  in  structure  in  the  mussel,  the  clam,  the  oyster,  and 
the  scallop.  The  internal  organs  also  have  the  same  general 
plan  of  structure  in  the  four  animals  named.  There  are  two 
adductor  muscles  in  the  mussel.  The  sexes  are  separate. 


FIG.  88.    Living  Fresh- Water  Mussel.     x| 

Development.  At  least  two  genera  of  fresh-water  mussels 
carry  their  young  in  their  gills,  which  are  open  dorsally  on 
the  inside.  Such  an  arrangement  is  necessary  because  the 
currents  in  rivers  all  go  one  way,  and  would  carry  the  help- 
less young  out  to  sea.  At  a  certain  stage  the  well-developed 
larvae  escape  from  the  brood-pouch  of  the  female  mussel 
and  fall  to  the  bottom.  Fish  "  nosing  "  along  the  river-bed 
touch  the  floating  byssus-thread  of  the  young  mussel,  which 
at  that  stage  is  called  the  glochidium  (Fig.  89).  The  thread 


THE  CLAM  AND   OTHER   BIVALVES 


173 


FIG.  89.    Larva  of  Mussel.    Much 
enlarged.    (After  Balfour) 

1,  shell;  2,  adductor  muscle;  3,  lar- 
val hook ;  4,  byssus-thread 


(Fig.  89,  4)  clings  to  the  surface  of  the  fish's  gill  or  skin,  and 
the  little  hook  (Fig.  89,  3)  on  the  edge  of  either  valve  sinks 
into  the  flesh.  For  several  weeks  the  glochidium  is  trans- 
ported on  the  fish,  during  which 
time  it  may  be  carried  into  an- 
other river,  even  by  way  of  the 
sea.  When  the  end  of  fixed 
development  comes,  the  protect- 
ing coat  is  dissolved  and  the 
little  mussel  falls  to  the  bottom 
again.  If  this  happens  in  a 
favorable  place,  it  burrows  into 
the  mud  and  begins  the  life  of 
its  adult  kin. 

Economic  Importance.  The  dis- 
tribution of  fresh-water  mussels  has  become  a  matter  of  con- 
siderable economic  importance,  especially  in  the  states  of 
Iowa  and  Illinois.  Factories  have  been  established  there  for 
the  purpose  of  making  pearl  buttons  from  the  valves.  True 
pearls  of  fine  quality  have  been  found  in  many  species  of 
mussels  in  all  parts  of  the  Mississippi  valley. 

The  opinion  has  been  held  by  many  that  if  grains  of  sand 
find  lodgment  between  the  mantle  and  the  valve  of  a  mussel 
or  an  oyster,  the  mantle  will  surround  the  particle  with 
layers  of  pearl,  like  the  substance  normally  secreted  by  the 
species  to  line  its  valves,  and  thus  form  pearls.  We  have  heard 
stories  of  these  valuable  products  being  formed  by  pearl-oyster 
fishermen,  who  inserted  grains  of  sand  between  the  valve 
and  the  mantle  of  the  famous  pearl-oyster  of  the  Arabian 
Gulf,  but  we  have  no  evidence  that  a  grain  of  sand  has  ever 
been  found  in  a  true  pearl.  Grains  of  sand  only  cause  rough 
spots  in  the  layer  of  mother-of-pearl. 

The  investigations  of  Professor  Jameson,  of  South  Africa,  in 
1902,  afford  the  first  conclusive  evidence  regarding  the  origin 


174 


GENERAL  ZOOLOGY 


of  pearls  in  the  common  edible  sea-water  mussel,  My'tilus 
ed'ulis  (in  Fig.  126).  A  trematode  parasitic  worm  (Fig.  Ill) 
in  the  larval  stage  creeps  between  the  valve  and  the  mantle- 
fold.  In  its  wanderings  it  starts  to  bore  through  the  mantle- 
fold.  The  tissue  is  soft,  but  the  parasite  may  rest  for  a  while 
among  the  loosely  connected  cells.  In  that  case  it  is  imme- 
diately surrounded  by  a  minute  fold  of  the  outer  epithelium 
(surface-cells)  of  the  mantle.  About  the  trematode  larva  as 
a  center  the  epithelium  (Fig.  90,  2)  begins  to  secrete  a  sub- 
stance which,  on  hardening, 
becomes  a  pearl  (Fig.  90,  5). 
Before  the  hardening  takes 
place  the  larva  may  move  to 
some  other  part  of  the  man- 
tle-fold. Again  it  may  be 
the  stimulus  for  producing  a 
pearl. 

Examination  of  pearls 
often  reveals  a  small  particle 
of  matter  about  which  the 
pearl  was  formed  in  layers. 
Professor  Jameson  thinks  the 
substance  at  the  center  of 
the  pearls  he  has  examined 

is  the  body-waste,  or  excrement,  of  the  parasite  (Fig.  90,  0), 
except  in  those  pearls  in  which  he  has  found  the  dead  body 
of  the  parasite  itself.  Even  the  temporary  presence  of  the 
parasite  is  a  sufficient  stimulus  for  the  production  of  a  pearl. 
The  pearl  may  get  so  large  that  it  breaks  through  the  outer 
epithelium  of  the  mantle-fold  and  becomes  attached  to  the 
valve  itself.  If  the  pearl  breaks  through  the  inner  (ciliated) 
epithelium  (Fig.  90,  3)  of  the  mantle-fold,  it  falls  into  the 
mantle-cavity,  and  finally  to  the  outside,  which  accounts  for 
the  fact  that  pearls  are  often  found  in  the  sand. 


FIG.  90.  Section  of  Mantle-Fold  of 
Mussel  showing  how  a  Pearl  is 
formed.  (After  Jameson) 

1,  cells  of  mantle ;  2,  external  epithelium 
of  mantle ;  .'$,  internal  (ciliated)  epi- 
thelium ;  4,  position  of  shell ;  5,  pearl ; 
6,  remains  of  parasite 


THE  CLAM  AND  OTHER  BIVALVES  175 

Relation  to  Environment.  The  distribution  of  Unio  com- 
planata  in  the  bed  of  a  river  is  determined  somewhat  defi- 
nitely by  the  position  of  the  strongest  current.  It  is  well 
known  that  in  a  crooked  river  the  main  current  does  not 
follow  the  middle  line  of  the  stream,  but  sweeps  from  bank 
to  bank  diagonally  across  the  middle.  The  greater  amount 
of  food  is  carried  along  by  the  swifter  water,  and  hence, 
unless  the  stream  is  too  swift,  the  mussels  find  it  advanta- 
geous to  range  themselves  along  the  line  of  the  most  abun- 
dant food-supply. 

Mussels  are  considered  by  some  to  be  of  great  service  to 
man  and  other  animals  because  of  their  habit  of  devouring 
the  decaying  organic  substances  so  abundant  in  rivers  which 
flow  past  large  cities.  There  is  good  reason  for  believing, 
however,  that  sewage  is  not  the  natural  food  of  mussels,  and 
that  they  will  flourish  better  in  water  of  natural  purity.  In 
fact,  it  has  been  positively  determined  that  mussels  do  not 
live  near  the  mouth  of  a  large  sewer. 

DEFINITION  OF  PELECYPODA 

The  four  animals  described  in  this  chapter  are  representa- 
tives of  a  class  called  by  various  authors  Lamellibranch'ia, 
Aceph'ala,  or  Pelecyp'oda  (Gr.  pelekys,  hatchet ;  pom  (pod), 
foot).  They  are  also  called  bivalves  because  the  shell  is 
in  two  pieces.  Lamellibranchia  signifies  that  the  animals 
have  gills  (branchige)  which  are  thin,  like  plates  (lamellae). 
Acephala  means  "  without  a  head." 

Pelecypoda  are  usually  bilaterally  symmetrical  animals  with 
an  external  skeleton  composed  of  two  more  or  less  nearly 
equal  valves.  They  have  no  internal  skeleton.  The  body  is 
without  a  head  and  is  not  divided  into  somites.  There  are 
no  segmented  appendages.  The  mantle-folds  surround  the 
body  proper  and  secrete  the  shell  substance.  Locomotion  is 


176  GENERAL  ZOOLOGY 

most  frequently  accomplished  by  a  single  muscular  organ, 
the  hatchet-shaped  foot.  The  valves  are  held  together  by  a 
hinge-ligament,  aided  sometimes  by  ridge-like  processes  fitting 
into  grooves.  The  valves  are  closed  by  one,  or  two,  adductor 
muscles. 

Four  palps  surround  the  mouth  and  carry  the  food  inward. 
The  oesophagus  is  short.  The  stomach  receives  the  secre- 
tion from  a  pair  of  digestive  glands.  The  intestine  coils 
several  times  and  ends  posteriorly.  The  circulatory  system 
is  nearly  complete.  There  are  two  auricles  and  one  ventricle 
in  the  heart.  The  pair  of  glands  of  the  reproductive  system 
in  male  and  female  individuals  seems  to  differ  only  in  micro- 
scopic structure.  In  some  species  the  sexes  are  separate.  In 
others  the  individuals  are  hermaphroditic  ;  that  is,  the  male 
and  female  sexual  glands  are  present  in  the  same  animal. 


CHAPTER  XV 
ALLIES  OF  THE  PELECYPODA :  MOLLUSCA 

The  frugal  snail,  with  forecast  of  repose, 
Carries  his  house  with  him  where'er  he  goes. 

CHARLES  LAMB. 

The  Pond-Snail.  Any  one  of  several  genera  and  species  of 
snails  that  live  in  fresh  water  might  be  given  the  name 
"pond-snail"  with  equal  accuracy.  The  one  represented  in 
Fig.  91  (Phy'sa  heterostro'pha)  is  quite  common  not  only  in 
ponds  but  in  rivers  as  well. 

Externally  the  most  noticeable  feature  of  the  pond-snail 
is  its  thin,  spiral  shell.  This  structure  is  made  of  the 
same  material  as  the  shell  of  bivalves.  A  large  portion  of  the 
animal's  body  fills  the  "  mouth  "  of  the  shell  and  extends 
spirally  toward  the  top.  The  direction  of  the  spiral  (or  spire) 
in  Physa  is  left-handed, — an  unusual  condition.  The  spire 
of  a  left-handed  shell,  starting  with  the  top  toward  the  ob- 
server, turns  contrary  to  the  movement  of  the  hands  of  a 
clock  ;  the  spire  of  a  right-handed  shell  turns  with  the  hands 
of  a  clock.  Between  the  shell  and  the  body-wall  lies  the 
mantle,  which  throughout  life  continues  the  growth  of  the 
shell  in  the  characteristic  spiral  direction. 

When  the  snail  is  disturbed  it  draws  its  shell  down  over 
the  entire  body;  but  while  feeding,  as  shown  in  the  picture, 
one  can  see  the  long,  muscular  foot,  broad  in  front  and 
pointed  behind.  The  anterior  region  of  the  body  is  the  head, 
more  or  less  sharply  marked  off  from  what  lies  behind.  The 
mouth  opens  beneath  an  extensile  upper  lip.  In  the  mouth 
is  a  short,  muscular  tongue,  on  which  grows  a  long  but 
minute  ribbon  of  rasp-like  teeth.  The  pond-snail  uses  this 

177 


178 


GENERAL  ZOOLOGY 


rasping-tongue,  running  it  in  and  out,  to  tear  into  bits  the 
soft  plant  tissues  on  which  it  feeds.  A  most  interesting 
experience  is  to  watch  a  pond-snail  as  it  crawls  slowly  up 


FIG.  91.  Group  of  Living  Pond-Snails.    Natural  size 

the  side  of  an  aquarium,  feeding  on  the  microscopic  plants 
as  it  goes.  At  such  times  one  can  see  the  mouth  open  and 
the  tongue  sweep  gracefully  out  and  in,  with  tiny,  rhythmic 
movements. 


ALLIES  OF  THE  PELECYPODA:  MOLLUSCA      179 

The  two  tentacles  are  organs  of  touch.  The  eyes  lie  one 
in  front  of  either  tentacle  at  its  base.  On  the  right  side, 
near  the  head,  are  the  single  openings  of  the  intestine,  the 
nephridium,  and  the  sexual  glands.  Also  on  the  right  side, 
and  partly  beneath  the  edge  of  the  shell,  is  an  aperture 
which  opens  and  closes  over  a  small  hollow  space  in  the 
body.  This  space  is  the  so-called  "lung"  of  the  pond-snail. 
The  lung  is  adapted  to  using  the  oxygen  of  the  atmosphere. 
Any  one  who  owns  an  aquarium  containing  snails  may  ob- 
serve them  crawling  up  the  side  of  the  vessel  on  their  way 
to  the  surface.  When  they  arrive  there  they  remain  for  some 
time,  opening  and  closing  the  lung  to  the  air.  In  aquaria 
which  have  a  supply  of  water-plants  growing  in  them,  the 
pond-snail  does  not  appear  to  go  to  the  surface  so  often.  It 
is  well  known  that  plants  give  off  oxygen.  Some  of  this 
oxygen  held  in  the  water  may  pass  through  the  snail's  skin, 
which  is  thin  and  soft.  The  waste  carbon  dioxide  of  the  snail 
is  discharged  into  the  water,  and  may  be  used  by  water- 
plants  as  raw  food-material. 

It  is  not  uncommon  to  see  a  pond-snail  crawling  upside 
down  at  the  surface  of  the  water.  The  explanation  of  this 
curious  phenomenon  is  the  same  as  the  explanation  of  how 
they  can  get  along  on  any  kind  of  a  surface.  Just  below  the 
mouth  is  the  opening  of  a  gland,  which  extends  through  the 
middle  of  the  foot  near  the  lower  surface.  If  we  look  closely 
at  the  inverted  snail,  we  can  see  the  wall  of  this  foot-gland 
contracting  with  a  wave-like  movement  in  the  act  of  sending 
the  secreted  mucus  (slime)  forward  to  be  poured  out  at  the 
opening.  The  mucus  spreads  out  a  short  distance  on  the 
water,  or  blade  of  water-plant,  or  submerged  pebble,  and 
forms  a  bed  over  which  the  animal  moves. 

When  the  foot  is  extended  in  locomotion  the  pond-snail 
weighs  less  than  an  equal  volume  of  water.  If  the  animal 
releases  its  hold  on  an  object  at  the  bottom,  it  floats  to  the 


180 


GENERAL  ZOOLOGY 


surface  quickly.  Conversely,  if  the  animal  voluntarily  (or 
under  visible  stimulus)  releases  its  hold  on  the  surface  of 
the  water,  it  draws  the  entire  body  into  the  shell  and  quickly 

falls  to  the  bottom.  In 
the  second  instance  the 
weight  of  the  snail's  body 
is  greater  than  the  weight 
of  an  equal  volume  of 
water.  One  might  well 
ask  why  the  pond-snail 
doesn't  migrate  up  and 
down  in  this  way  habit- 
ually. We  can  only  say 
that  perhaps  the  sudden 
change  of  pressure  from 
a  great  to  a  less  amount 
in  going  up,  and  from  a 
small  to  a  greater  amount 
in  going  down,  is  not  so 
favorable  as  a  slower  rate 
FIG.  02.  Mucus-Threads  of  Pond-Snail  of  change  would  be. 
(Limnoza)  in  Water.  Reduced.  (After  ° 

Kew)  We   find   some    confir- 

mation of  this  theory  in 

the  existence  of  vertical  threads  of  mucus  in  snail  aquaria 
and  in  ponds  (Fig.  92).  A  snail  on  leaving  the  bottom  may 
pour  out  mucus  from  its  foot- gland  in  the  usual  way.  The 
mucus  fastened  at  the  bottom  will  *be  paid  out  in  the  form 
of  a  thread,  as  the  animal  floats  upward,  slowly  held  back  by 
this  thread.  When  the  snail  gets  to  the  surface  the  thread  is 
moored  there  in  a  patch  of  mucus.  Each  thread  thus  formed 
becomes  a  permanent  pathway,  tending  to  increase  in  thick- 
ness and  in  strength  as  the  snail  makes  use. of  it. 

In  the  spring  and  summer  months  the  pond-snail  lays  eggs 
even  in  captivity.    The  sexual  gland  is  hermaphroditic,  hence 


ALLIES  OF  THE  PELECYPODA :  MOLLUSCA     181 


every  individual  is  likely  to  deposit  eggs.  The  eggs  may  be 
found  on  the  branches  of  water-plants,  or  even  on  the  per- 
pendicular sides  of  a  glass  aquarium,  imbedded  in  an  ellip- 
tical, clear,  gelatinous  mass  from  two  millimeters  to  six 
millimeters  long.  In  each  mass  from  five  or  six  to  twenty- 
five  eggs  may  be  distinguished. 

The  Land-Snail.  One  of  the  commonest  of  the  land-snails  in 
America  is  the  one  shown  in  Fig.  93  (He'lix  nebulo'sa).  'Like 
its  many  kindred  species  of  the  genus  Helix,  it  lives  in 
moist,  protected  places  during  the  day,  and  comes  out  to 
feed  at  night.  Frequently  it  leaves  its  hiding-place  in  cloudy, 
damp,  but  not  in  rainy, 
weather. 

In  general  features,  the 
organs  to  be  noted  on  the 
exterior  of  this  animal  are 
the  same  as  in  the  pond- 
snail.  The  openings  of  all 
the  internal  organs 
occur  in  the  same 
position  in  both 
animals.     There 
are  four  tentacles 
in   Helix,  —  an 
upper,    long    pair 
bearing  the  eyes, 
and  a  lower,  short 
pair,  which   are 
the    organs    of 
touch.    The  edge  of  the  mantle  is  thickened  to  form  a  collar. 

In  the  fall  of  the  year,  about  the  time  of  frost,  the  land- 
snail  ceases  to  eat,  becomes  inactive,  and  makes  preparation 
for  the  winter's  sleep,  or  hibernation.  Crawling  to  the  pro- 
tected side  of  an  object  which  has  a  smooth  surface,  the 


FIG.  93.  Living  Land-Snail.    Natural  size 


182  GENERAL  ZOOLOGY 

animal  withdraws  into  its  shell,  allowing  the  edge  to  fit 
closely  to  the  object.  Then  certain  glands  in  the  collar 
secrete  mucus,  which  flows  from  all  sides  over  the  under 
surface  of  the  foot,  between  it  and  the  supporting  surface. 

When  the  membrane  dries  it  has  the  appearance  of  stiff, 
oiled  paper  of  considerable  toughness.  It  is  called  the  epi- 
phragin. It  is  supposed  that  the  epiphragin  aids  in  retaining 
the  body-heat  during  the  four  to  six  months  of  sleep.  Metab- 
olism (see  p.  206)  continues  through  all  that  time,  but  at  a 
much  reduced  rate.  A  very  small  hole  is  to  be  found  in  the 
epiphragin,  in  one  species  of  Helix  at  least,  just  below  the 
lung-aperture.  Through  this  oxygen  and  carbon  dioxide  may 
continue  to  pass.  With  the  returning  warmth  of  spring  the 
snail  bursts  the  epiphragm  and  recommences  active  life. 

The  Garden-Slug.  The  particular  species  of  garden-slug, 
the  habits  of  which  are  suggested  in  Fig.  94,  is  Li'max 
max'imus.  It  is  a  native  of  Europe,  not  of  America,  and 
since  its  introduction  here  has  become  a  more  unwelcome 
guest  in  greenhouses  than  any  other  species  of  slug  or  snail. 
As  yet  it  is  not  widely  distributed  from  the  vicinity  of 
New  York  and  Boston. 

In  brief  terms  we  may  describe  a  slug  as  a  snail  with  a 
rudimentary  shell.  The  elliptical  plate  of  muscle  on  the 
dorsal  surface  of  Limax  is  all  that  is  left  of  the  mantle.  In 
the  process  of  degeneration,  which  we  may  well  suppose  has 
occupied  thousands  of  years,  the  mantle  folded  back  over 
the  shell  as  the  latter  decreased  in  size.  If  we  examine  the 
interior  of  the  mantle,  we  find  a  thin,  calcareous  plate,  which 
is  undoubtedly  the  rudimentary  shell. 

Aside  from  the  difference  in  the  size  and  form  of  the  shell, 
Limax  maximus  and  Helix  nebulosa  are  very  much  alike. 
The  body  of  Limax  is  straightened  out,  but  the  organs  which 
in  Helix  have  openings  on  the  right  side  of  the  body  also 
have  openings  on  the  right  side  in  Limax.  These  are  the 


ALLIES  OF  THE  PELECYPODA :  MOLLUSCA     183 


generative  opening  just  back  of  the  right  eye-stalk,  the  anus, 
and  the  nephridial  opening  near  the  lung-aperture.  The 
garden-slug,  like  the  snails,  has  a  rasping-tongue. 

If  a  person  examines  in  daylight  the  under  side  of  boxes  or 
bunches  of  straw  that  usually  collect  about  a  greenhouse,  he 
will  find  within  the  range 
of  the  animal's  distribution 
many  specimens  with  their 
heads  contracted  to  the 
body,  holding  to  the 


surface  of  the 
thing  which 
conceals  them.  Frequently 
after  a  night's  forage  on  the 
tender  parts  of  greenhouse  plants, 
they  go  no  farther  away  than  the 
bottom  of  the  flower-pot.  Reliable 
observers  have  marked  specimens 
and  have  found  that  these  creatures  return  night  after  night 
to  a  particularly  succulent  plant,  such  as  the  Amaryllis  in  the 
picture.  It  is  thought  by  some  that  their  "  sense  of  direction" 
lies  in  the  ability  to  smell  their  food-plant.  Some  authors 
believe  that  the  organ  of  smell  lies  at  or  near  the  end  of 


FIG.  94.   Garden-Slug  feeding 
at  Night,     x  i 


184  GENERAL  ZOOLOGY 

the  eye-stalk;  others  are  inclined  to  think  that  the  animal 
has  a  more  definite  organ  of  smell  in  the  osphradium.  This 
organ  occurs  on  the  mantle-edge  near  the  lung-aperture. 

The  ravages  of  Limax  maximus  are  not  serious,  if  the 
florist  does  not  allow  refuse  to  collect  about  his  buildings. 
Many  adopt  the  method  of  scattering  ashes  or  cinders  about 
the  plants  to  be  especially  protected.  A  slug  crawling  into 
such  an  obstruction  is  stimulated  by  the  dryness  of  the  ashes, 
or  the  roughness  of  the  cinders,  to  secrete  mucus  from  the 
glands  that  occur  in  the  skin.  This  mucus  is  like  that  which 
is  secreted  from  its  foot-gland  while  crawling.  Owing  to  the 
unusual  amount  of  mucus  given  off  at  such  times,  the  animal 
dies  from  exhaustion,  and  from  suffocation  by  the  drying  of 
its  skin. 

From  the  beginning  of  September  to  the  end  of  November 
Limax  maximus  lays  its  eggs  in  its  place  of  hiding.  The  eggs 
have  about  one  half  the  diameter  of  dried  peas.  They  are  quite 
spherical.  The  shell  is  translucent  and  is  tough  and  membra- 
nous. Twenty-five  or  thirty  eggs  are  deposited  at  one  time, 
and  left  on  the  ground  in  a  loose,  agglutinated  mass.  The 
embryos  of  the  early  eggs  hatch  within  two  or  three  weeks, 
while  eggs  deposited  late  probably  do  not  hatch  until  the 
following  spring.  The  garden-slug  is  hermaphroditic.  The 
eggs  and  spermatozoa  in  each  individual  mature  at  differ- 
ent times,  and  consequently  the  union  of  two  individuals  is 
necessary  for  the  fertilization  of  the  eggs. 

Garden-slugs  that  live  out-of-doors  burrow  into  the  ground 
and  curl  up  when  the  coldest  weather  comes.  Those  in  green- 
houses remain  active  throughout  the  year. 

The  Oyster-Drill.  A  few  minutes'  walk  along  almost  any 
pebbly  beach  between  Florida  and  the  Gulf  of  St.  Lawrence 
would  afford  a  collector  the  opportunity  of  observing  the  sub- 
ject of  this  description,  the  oyster-drill  (Urosal'pinx  cine'rea, 
Fig.  99).  In  such  a  walk  the  artist  discovered  the  unfortunate 


ALLIES  OF  THE  PELECYPODA :  MOLLUSCA     185 

periwinkle  at  the  left  of  the  picture,  with  the  oyster-drill  of 
the  foreground  engaged  in  devouring  the  soft  parts  of  its 
victim  through  the  hole  made  in  the  thick  shell.  For  the 
purposes  of  illustration  the  oyster-drill  was  placed  on  another 
periwinkle  in  the  same  position  it  occupied  on  the  first  when 
discovered.  In  deep  water  the  oyster-drill  devotes  itself  to 
the  business  which  gave  it  the  name  it  bears.  There  are 
several  other  species  of  snails,  however,  which  have  the  same 
habit  of  boring  through  the  oyster's  valves  and  feeding  on 
the  soft  parts. 

The  oyster-drill  has  organs  not  found  in  the  snails  already 
described  in  this  chapter.  In  a  little  groove  in  the  "mouth" 
of  the  shell  lies  a  small  tube  called  the  siphon,  which  carries 
water  to  a  gill-chamber,  where  the  blood  is  supplied  with 
oxygen.  Another  organ  is  a  horny  plate  growing  on  top  of 
the  posterior  end  of  the  foot.  When  the  foot  is  withdrawn 
into  the  shell,  the  horny  plate,  which  is  called  the  operculum 
(a  lid,  or  cover),  is  drawn  into  the  mouth  of  the  shell.  The 
operculum  is  of  great  service  to  the  animal  in  keeping  out 
unwelcome  visitors. 

The  oyster-drill,  in  common  with  all  other  species  of  snails 
that  have  their  habitat  on  the  seashore,  possesses  a  very  thick 
shell,  adapted  to  the  severe  conditions  of  life  there.  The 
sand  and  pebbles  are  constantly  shifting  under  the  pressure 
of  the  waves,  and  only  those  snails  that  have  thick  shells  can 
endure  the  conditions. 

The  Periwinkle.  The  periwinkle,  a  littoral  (shore)  species 
(Littori'na  litto'rea,  Fig.  99),  is  a  native  of  Europe.  Its  pres- 
ence here  is  accounted  for  by  the  supposition  that  specimens 
were  accidentally  thrown  in  with  the  gravel  used  for  ballast 
on  ocean-going  vessels,  and  thrown  out  again  when  the  vessel 
reached  its  port  in  America.  The  first  specimens  noticed  in 
America  by  conchologists  (students  of  shells)  were  reported  at 
Halifax,  Nova  Scotia,  in  1857.  Since  that  time  the  periwinkle 


186 


GENERAL  ZOOLOGY 


has  been  making  its  way  down  the  coast.  It  may  now  be  found 
in  southern  waters.  The  new  home  in  America  seems  to  be 
especially  favorable  for  the  periwinkle,  for  on  the  rocky  coast 
of  New  England  there  are  so  many  of  them  that  on  first 
impression  there  appears  to  be  no  other  species. 

The  periwinkle  depends  on  plant-food  altogether.  It  is 
reported  that  the  oystermen  of  Whitstable,  England,  at  the 
mouth  of  the  Thames  River,  collect  these  snails  in  large  quan- 
tities and  throw  them  over  the  oyster-beds  in  order  to  be  rid 
of  the  excess  growth  of  seaweeds. 

On  account  of  its  great  abundance  the  periwinkle  is  much 
used  as  an  article  of  human  food  in  England  and  011  the 
Continent.  It  is  one  of  the  many  species  of  snails  and  slugs 
used  as  food,  especially  by  the  French  people. 

The  Nudibranch.  The  strange-looking  creature  shown  in 
Fig.  95,  Dendrono'tus  arbor  es'cens,  is  to  be  found  on  seaweeds 

and  under  submerged 
rocks  along  the  North 
Atlantic  coast. 

The  general  form  of 
a  slug  is,  in  this  animal, 
modified  by  the  occur- 
rence of  tree-like  proc- 
esses growing  on  the 
upper  part  of  the  body, 
whence  the  generic  and 

specific  names.     These 

Fio.96.    Photograph  of  Living  Nudibranch.  gseg    are    oalled 

Natural  size 

cer-ata,    and    to    some 

extent  are  used  in  respiration.  Being  thin,  oxygen  can  pass 
into  the  animal  through  them,  and  the  waste  carbon  dioxide 
can  pass  out.  The  group  of  animals  to  which  they  belong 
is  called  Nudibran' chia,  in  reference  to  the  fact  that  their 
gills  are  naked.  There  is  no  indication  of  a  rudimentary 


ALLIES  OF  THE  PELECYPODA :  MOLLUSCA     187 

shell  in  Dendronotus,  but  the  presence  of  other  organs, 
including  the  rasping-tongue,  proves  their  relationship  to  the 
garden-slug. 

Nudibranchs  deposit  their  eggs  in  protected  places,  fasten- 
ing them  with  mucus  against  rocks  and  seaweeds.  One  may 
recognize  the  egg-mass  of  Dendronotus  by  its  salmon-pink 
color  and  its  coiled  arrangement. 

The  color  of  this  animal  is  rich  brown ;  the  same  colors 
occur  in  its  immediate  environment.  Quite  as  valuable  as 
the  color-resemblance,  in  protecting  the  nudibranch  against 
ravenous  fish,  is  the  marked  similarity  of  the  cerata,  in  form, 
to  the  delicate  branches  of  certain  seaweeds.  The  slowness  of 
the  animal's  movements  must  also  aid  it  in  escaping  notice. 

Definition  of  Gasteropoda  (Gr.  gaster,  stomach  ;  pous 
(2>od),  foot).  The  class  represented  by  the  snails,  the  slug, 
and  the  nudibranch  is  given  the  name  Gr  aster  op' o  da.  The 
class-name  is  only  figuratively  correct.  The  ventral  surface, 
not  the  stomach,  is  modified  to  form  a  locomotor  organ, 
the  foot. 

An  important  characteristic  of  the  Gasteropoda  is  the 
unsymmetrical  arrangement  of  organs.  With  the  exception 
of  the  mouth  and  the  opening  of  the  mucus-gland,  all  the 
openings  of  the  body  are  on  the  right  side,  even  in  cases  like 
the  slug  and  nudibranch,  where  the  general  form  of  the  body 
is  bilaterally  symmetrical.  The  asymmetry  (lack  of  symme- 
try) of  the  organs  is  directly  connected  with  the  existence 
(present  or  past)  of  a  shell.  When  a  shell  occurs  it  is  com- 
posed of  one  piece,  and  the  characteristic  form  is  spiral.  A 
shell-forming  organ,  the  mantle,  is  usually  present. 

The  body  of  Gasteropoda  is  not  divided  into  somites,  but 
the  head  is  slightly  marked  off  from  the  rest  of  the  animal, 
and  is  provided  with  eyes  and  unsegmented  tentacles.  A 
tongue-like  organ  bears  a  ribbon  of  minute  teeth  for  tear- 
ing food. 


188  GENERAL  ZOOLOGY 

The  Squid.  In  the  waters  of  the  Grand  Banks  of  New- 
foundland and  southward  to  Massachusetts  the  members  of 
a  species  of  squid,  Ommas'trephes  illecebro'sa  (Fig.  96),  occur 
in  great  numbers.  They  capture  small  fishes,  and  are  them- 
selves prey  for  cod  and  other  large  fishes. 

The  body  of  the  squid  is  composed  of  a  head  and  a  slender, 
conical  portion,  the  former  having  a  pair  of  large,  movable 
eyes  (Fig.  96,  G).  Arising  from  the  head-region  are  ten  long, 
club-shaped  arms  (Fig.  96,  1),  corresponding  morphologically 
to  the  foot  of  the  Pelecypoda  and  the  Gasteropoda.  Two  of 
the  arms  are  longer  than  the  other  eight,  but  all  are  provided 
on  part  of  the  inner  surface  with  many  sucking-disks,  adapted 
to  holding  the  prey.  The  mouth  has  two  horny  jaws,  resem- 
bling in  appearance  the  bill  of  a  parrot  turned  upside  down. 
The  tongue  is  adapted  to  rasping. 

The  conical  portion  of  the  body  is  the  mantle  (Fig.  96,  2), 
highly  modified  by  the  existence  of  strong,  muscular  bands. 
Part  of  the  space  within  the  muscular  mantle  is  occupied  by 
the  internal  organs  inclosed  in  a  body-cavity.  The  remainder 
of  the  space,  the  mantle-cavity  itself,  connects  with  the  out- 
side by  a  narrow  opening  (Fig.  96,  5),  at  either  side  of  the 
neck,  and  also  by  the  siphon  (Fig.  96,  4).  A  pair  of  feather- 
shaped  gills,  one  attached  to  either  side  of  the  body,  lies  in 
the  mantle-cavity.  Imbedded  in  the  tissue  of  the  mantle, 
on  the  side  opposite  the  surface  shown  in  the  figure,  there 
is  a  long,  pen-shaped  structure  composed  of  chitinous  mate- 
rial. This  is  supposed  to  be  the  homologue  of  the  shell  of 
Pelecypoda  and  Gasteropoda.  The  sexes  are  separate. 

In  locomotion  the  squid  contracts  and  relaxes  the  circular 
muscles  of  the  mantle,  alternately  decreasing  and  increasing 
the  volume  of  the  mantle-cavity.  During  relaxation,  water 
enters  the  mantle-cavity  at  the  sides  by  the  neck,  a  valve 
in  the  siphon  being  closed;  in  contraction  the  valves  at 
the  side  openings  are  closed  and  the  water  is  discharged 


FIG.  96.  Photograph  of  Squid,     x  -£ 
1,  teutacle;  2,  mantle;  3,  mantle-fin;  4,  siphon;  5,  incurrent  opening ;  6,  eye 


189 


190  GENERAL  ZOOLOGY 

through  the  siphon.  The  siphon  may  be  directed  forward 
or  backward  at  will.  If  it  is  bent  in  the  direction  of  the 
arms,  as  it  commonly  is,  the  squid  during  strong  contraction 
of  the  mantle  darts  backward  "  with  the  speed  of  an  arrow," 
balanced  and  steered  by  the  aid  of  the  double  mantle-fin 
(Fig.  96,  3). 

In  the  squid's  most  rapid  locomotion  the  mantle-fins  are 
folded  toward  the  body.  In  slower  movements  a  wave-like 
flapping  of  the  fins  supplements  the  jets  from  the  siphon. 
So  skillfully  manipulated  are  the  mantle-fins,  and  the  mantle- 
point  itself,  in  turning  to  one  side  or  the  other,  and  in  going 
up  or  down,  that  one  marvels  at  the  wonderful  adaptations 
of  an  animal  that  has  its  "steering-gear"  in  front,  instead  of 
behind,  its  principal  "  engine." 

While  at  rest  on  the  bottom  of  an  aquarium  the  squid  ex- 
tends its  two  long  arms  to  the  bottom,  bent  akimbo,  appar- 
ently to  keep  the  siphon  and  the  two  lateral  mantle-openings 
away  from  the  sand.  The  mantle  forms  the  third  point  of 
support  in  the  resting  attitude.  Water  may  then  be  drawn 
into  the  mantle-cavity,  and  expelled  again,  in  the  normal 
process  of  respiration. 

No  more  beautiful  example  of  rapid  color-change  can  be 
witnessed  than  the  one  going  on  constantly  in  the  skin  of 
captive  squids.  From  bluish  white  the  color  may  change  on 
the  instant  to  mottled  red  or  brown.  The  change  may  be 
sudden  and  complete,  or  the  colors  may  fluctuate  repeatedly 
from  one  shade  to  another  and  shimmer  over  the  surface  seem- 
ingly as  rapidly  as  the  controlling  nerves  can  act.  Observers 
who  have  been  fortunate  enough  to  come  upon  a  "  school " 
of  squids  in  a  harbor  have  been  puzzled  by  the  sudden  disap- 
pearance of  the  animals.  In  times  of  danger  the  ability  to 
change  color  to  resemble  the  environment  must  be  of  consid- 
erable value  to  them  in  escaping  the  notice  of  enemies,  as 
well  as  useful  in  coming  unseen  into  a  school  of  small  fish. 


ALLIES  OF  THE  PELECYPODA :  MOLLUSCA     191 


Another  and  still  more  effective  means  of  escaping  from 
the  attack  of  a  superior  enemy  is  employed  by  the  squid  when 
driven  to  its  last  resource.  It  has  in  its  body-cavity  a  sac 
which  secretes  a  black,  inky  fluid.  A  tube  from  the  ink-sac 
passes  to  the  siphon,  and  in  the  moment  of  need  the  sac  and 
the  muscular  mantle  contract  and  force  the  black,  confusing 
fluid  into  the  water.  The  squid  then  has  a  chance  to  escape. 

The  Chambered 
Nautilus.  Almost 
the  sole  represent- 
ative of  a  once 
numerous  race 
living  in  the 
depths  of  the  sea, 
the  chambered 
or  pearly  nautilus 
(Nau'tilus  pom- 
pil'ius,  Fig.  97) 
now  has  a  restrict- 
ed distribution  in 
the  vicinity  of  cer- 
tain South  Pacific 
islands,  such  as 
New  Guinea  and 
the  Philippines.  Nautilus  lives  on  the  bottom,  usually  in 
water  from  one  hundred  to  seven  hundred  meters  deep  (three 
hundred  and  twenty-five  to  twenty-three  hundred  feet). 

The  shell  of  Nautilus  is  divided  into  compartments  by 
cross-partitions.  Each  of  these  compartments  represents  a 
space  in  which  the  animal  lived  at  successive  stages  in  its 
growth.  The  chambers  of  the  entire  series  are  filled  with  air 
and  are  connected  by  a  slender  tube  called  the  siphuncle^ 
borne  in  a  thin-walled,  calcareous  tube  (Fig.  97,  11  ).  The 
siphuncle  is  a  part  of  the  animal's  body  proper.  A  mantle 


FIG.  97.  Nautilus.    Reduced.    (After  Ludwig) 

1,  mantle ;  2,  dorsal  fold  of  mantle ;  3,  tentacles ;  4,  head- 
fold  ;  5,  eye  ;  6,  siphon ;  7,  position  of  nidamental 
gland ;  8,  shell-muscle ;  9,  living  chamber ;  10,  parti- 
tions between  chambers;  11,  siphuncle  with  tube 

(From  Hertwig-Kingsley's  General  Zoology) 


192  GENERAL  ZOOLOGY 

lies  within  the  outermost  chamber  of  the  shell  and  extends  a 
dorsal  fold  outward  against  the  old  part  of  the  shell.  When 
the  animal  is  contracted  into  the  outer  chamber  a  thick  brown 
hood  conceals  it  from  view.  When  the  head  is  extended  two 
large  eyes,  about  forty  tentacles  (arms),  and  a  siphon  are  vis- 
ible. The  mouth  is  provided  with  a  beak  like  that  of  the 
squid,  and  with  a  rasping-tongue.  Inside  the  mantle-cavity 
there  are  four  gills.  There  is  no  ink-sac.  Another  difference 
between  the  chambered  nautilus  and  the  squid  is  the  entire 
absence  in  the  former  of  the  ability  to  change  color.  The 
sexes  are  separate,  as  in  the  squid. 

The  food  of  the  animal  consists  of  deep-water  bivalves.  In 
obtaining  food  Nautilus  probably  uses  the  tentacles.  Although 
these  organs  have  no  sucking-disks,  as  the  squid  has,  the 
inner  edges  of  the  tentacles  appear  to  have  the  power  of  flat- 
tening against  an  object  and  of  holding  it  effectively. 

Owing  to  the  fact  that  Nautilus  lives  at  great  depths,  we 
know  very  little  concerning  its  habits.  Professor  Willey,  of 
England,  and  Professor  Dean,  of  Columbia  University,  have 
studied  the  live  Nautilus  recently  (1895  to  1901),  and  have 
published  reports  on  that  subject.  Nautilus  is  accustomed  to 
a  great  pressure  of  water  and  low  temperature.  When  brought 
to  the  surface  in  traps  it  could  scarcely  be  expected  to  act 
naturally.  However,  it  seems  reasonable  to  believe  that  the 
method  of  locomotion  would  not  be  affected.  It  swims  by 
means  of  a  jet  of  water  from  the  siphon,  and  the  convex  sur- 
face of  the  shell  parts  the  water  in  its  progress. 

Oliver  Wendell  Holmes,  in  his  poem,  The  Chambered  Nau- 
?,  thus  refers  to  the  phenomena  of  its  growth  : 

Year  after  year  beheld  the  silent  toil 

That  spread  his  lustrous  coil ; 

Still,  as  the  spiral  grew, 
He  left  the  past  year's  dwelling  for  the  new, 
Stole  with  soft  step  its  shining  archway  through, 

Built  up  its  idle  door, 
Stretched  in  his  last-found  home  and  knew  the  old  no  more. 


ALLIES  OF  THE  PELECYPODA :  MOLLUSCA     193 


Fossil  Relatives  of  Nautilus.  Many  millions  of  years  ago,  in 
the  early  history  of  the  earth,  the  most  ancient  of  the  imme- 
diate ancestors  of  Nautilus  lived.  Paleon- 
tologists (students  of  fossils)  have  given  its 
fossil  (Fig.  98)  the  name  Orthoc'eras  (Gr. 
orthos,  straight;  keras,  horn).  The  strongest 
evidence  we  have  that  Orthoceras  is  a  rela- 
tive of  Nautilus  is  the  series  of  chambers 
joined  by  the  siphuncle.  We  know  nothing 
of  the  structure  of  the  soft  parts  of  Orthoc- 
eras, but  paleontologists  have  made  draw- 
ings to  show  how  Orthoceras  probably 
appeared.  From  the  study  of  fossils  in 
later  layers  of  the  earth's  crust  we  know 
that  the  group  of  nautiloids  (Nautilus-like 
animals)  grew  to  be  of  large  size,  and  to 
have  their  shells  coiled  more  and  more  to 
the  close  coil  of  the  present-day  Nautilus. 
All  of  the  hundreds  of  species  of  nautiloids, 
except  four  species  of  Nautilus,  disap- 
peared as  living  things  ages  before  man 
came  into  existence  upon  the  earth. 

Definition  of  Cephalopoda  (Gr.  kephale, 
head ;  pous  (pod),  foot).  Ommastrephes, 
Nautilus,  and  Orthoceras,  because  of  their 
structural  relationship,  belong  in  a  class 
together,  the  Ceplialop'oda. 

In  this  class  the  body  has  a  distinct  head. 
No  part  shows  indications  of  being  divided 
into  somites.  The  head  has  two  large  eyes. 

The  mouth  is  surrounded  by  divisions  of    FIG.  98.  Fossil  Orthoc- 
.  P  ,  eras.     Reduced, 

the  primitive  foot,  called  arms  or  tentacles.         (After  Blake) 

These   divisions   of  the    foot   either  have 
sucking-disks  for  holding  on,  or  smooth  surfaces  which  per- 
form the  same  function.    In  the  mouth  there  is  a  parrot-like 


194 


GENERAL  ZOOLOGY 


beak  and  a  rasping-tongue.  A  shell-forming  mantle  either 
incloses  the  shell,  as  in  the  squid,  or  lies  beneath  it,  as  in 
Nautilus  and  Orthoceras. 

There  are  two  gills  in  the  mantle-cavity  in  the  squid,  and 
four  in  Nautilus.  A  siphon  is  present  in  all  the  examples 
described.  The  sexes  are  separate. 

Definition  of  Mollusca  (Lat.  molluscus,  soft).  The  phylum 
Mollus'ca  includes  five  classes.  For  the  purpose  of  elemen- 
tary study  the  most  important  ones  are  the  Pelecypoda,  the 
Gasteropoda,  and  the  Cephalopoda. 

On  the  basis  of  the  facts  presented  in  this  and  the  pre- 
ceding chapter,  we  may  formulate  the  following  statement 
concerning  the  phylum.  Mollusca  are  soft-bodied  animals 
provided  usually  with  a  hard,  calcareous,  partly  chitinous 
shell,  which  in  some  forms  occurs  on  the  exterior,  and  in 
others  is  partially  or  completely  inclosed  by  a  sheet  of  shell- 
forming  muscular  tissue,  the  mantle.  The  body  proper  is 
never  divided  into  somites,  and  the  appendages  are  never 
segmented. 


FIG.  99.  Living  Oyster-Drill  and  Periwinkle,     x  f 


CHAPTER   XVI 
THE  EARTHWORM 

I  guess  the  pussy-willows  now 
Are  creeping  out  on  every  bough 

Along  the  brook ;  and  robins  look 
For  early  worms  behind  the  plough. 

HENRY  VAN  DYKE,  An  Angler's  Wish. 

Habitat  and  Distribution.  The  animal  which  is  the  subject 
of  this  chapter  is  distributed  widely  throughout  the  world. 
The  more  familiar  species  live  in  the  soil,  where  their  burrows 
extend  obliquely  downward,  sometimes  many  feet.  One  rather 
common  species,  Alloloboph' ora  fce'tida,  marked  by  red  and 
dark  bands  of  color,  lives  in  manure  heaps.  When  irritated 
it  gives  off  an  offensive  odor,  whence  its  specific  name.  The 
species  best  known  in  America  is  Lumbri'cus  terres'tris.  It  is 
found  in  small  cylindrical  burrows,  which  it  makes  in  the  soil 
wherever  it  is  not  too  dry  or  too  sandy.  In  spite  of  the  usual 
habit  of  living  in  the  earth,  these  animals  can  live  for  many 
days  in  a  body  of  water  without  great  discomfort.  Repre- 
sentatives of  the  many  species  and  the  few  genera  of  earth- 
worms are  found  in  practically  all  places  from  Arctic  to 
Antarctic  regions,  including  isolated  oceanic  islands. 

External  Structure.  T-  external  structure  the  body  of  the 
earthworm  is  very  simple.  The  anterior  end  is  slender  and 
pointed  when  extended  in  life,  and  the  posterior  region  is 
flattened  above  as  well  as  below.  The  somites  of  the  anterior 
region  differ  also  from  those  in  the  posterior  region  in  being 
longer.  There  is  no  head,  no  thorax,  and  no  abdomen.  There 
are  no  appendages  except  bristles,  almost  microscopic  in  size, 
which  occur  in  rows  on  the  ventral  surface  of  every  somite 

195 


196  GENERAL  ZOOLOGY 

except  a  few  at  the  anterior  end.  The  openings  of  the  body 
are  themouth'&t  the  anterior  end  just  beneath  the  prostomium 
(lip),  the  anus  at  the  posterior  end,  and  various  openings  on 
the  ventral  surface,  which  are  connected  with  internal  organs 
to  be  described  later.  The  earthworm  has  no  eyes,  yet  it 
knows  of  the  existence  of  light,  and  shuns  intense  light;  it 
has  no  ears,  but  it  becomes  aware  of  the  approach  of  an  enemy 
by  the  jar  communicated  through  the  soil.  In  the  mature 
earthworm  a  thick  band,  consisting  of  the  thickened  body- 
wall,  is  visible  at  about  one  third  the  length  of  the  animal 
from  the  anterior  end.  This  is  called  the  ditellum. 

PHYSIOLOGICAL  PROCESSES 

The  internal  anatomy  of  the  earthworm  seems,  on  reference 
to  Fig.  100,  to  be  very  complicated,  but  we  shall  find  that 
each  system  of  organs  has  well-defined  uses.  From  the  study 
of  the  internal  organs  represented  here  we  shall  learn  some- 
thing of  the  uses  of  internal  organs  in  general;  and  we 
shall  endeavor  to  understand  more  fully  the  nature  of  physi- 
ological processes,  which  have  been  briefly  referred  to  in  the 
chapter  on  the  locust.  We  have  already  become  familiar  with 
the  organs  in  which  these  processes  take  place  under  the 
names  digestive  system,  circulatory  system,  respiratory  sys- 
tem, excretory  system,  and  the  like. 

Digestion.  The  first  division  of  the  digestive  system  of  the 
earthworm  is  the  mouth  (Fig.  100,  6),  followed  by  the  pharynx 
(Fig.  100,  7),  the  latter  having  a  very  thick  muscular  wall. 
The  pharynx  can  be  protruded  slightly  or  retracted,  and  the 
cavity  enlarged  by  strands  of  muscle-fibers  which  extend  to 
the  body-wall  (Fig.  100,  9).  Food,  consisting  of  particles  of 
leaves,  animal  tissues,  and  even  soil,  is  drawn  into  the  pharynx 
by  the  sucking  action  which  takes  place  when  the  cavity  of 
the  pharynx  is  enlarged.  The  food  passes  directly  through 


.         eN-~ 

a  s  1  ?  a  8  a 

PH   E     SH.^     bJD    •-  'V 
' 


<VJ      S 


198  GENERAL  ZOOLOGY 

the  esophagus  (Fig.  100,  10,  11).  Before  the  ingested  (swal- 
lowed) food  reaches  the  crop  (Fig.  100,  12)  the  secretion,  and 
sometimes  even  hard  particles  from  the  calciferous  glands 
(Fig.  100,  15, 16),  mixes  with  it  and  probably  serves  to  neutral- 
ize whatever  acid  may  be  present,  and  helps  to  maintain  the 
contents  of  the  oesophagus  in  an  alkaline  condition,  so  that 
the  digestive  fluid  of  the  intestine  (Fig.  100,  14),  which  is 
alkaline  in  chemical  nature,  can  act  without  interference. 
The  crop  is  a  temporary  reservoir  for  the  food,  and  the  gizzard 
(Fig.  100,  13)  is  the  only  place  in  the  entire  digestive  system 
adapted  for  dividing  large  particles  of  food  into  minute  pieces. 
Earthworms  are  known  to  swallow  small,  rough  pebbles,  and 
even  sharp  pieces  of  glass,  for  the  purpose  of  using  them  in 
the  gizzard  to  grind  into  bits  other  particles  which  are  swal- 
lowed as  food.  The  strong  muscles  in  the  wall  of  the  gizzard, 
by  corseting,  grind  the  contents  together,  and  every  particle 
is  worn  smaller. 

The  process  c      LigestiOn  in  the  earthworm  begins  "rhmi. 
son  seizing  food  with  its  lip,  the  animal  pours  out  a  secretion 
from  glands 'iii  "tire ^hurvnx.    Digestion  continues  .as  the  food 
is  being  drawn  into  the  pharynx,  ana  Wiiiie  on  "its  \va_>  fh  rough 
the  oesophagus.    Experiments  with  the  digestive  fluid  of  etrth- 
worms  indicate  that  it  has  a  chemical  action  on  the  thivt 
principal  classes  of  organic   foods,  namely,  proteids,  carfa 
hydrates,  and /ate.    The  proteids  which  the  earthworm  T 
be  likely  to  devour  are  bits  of  muscle  of  very  small  animals, 
and  protoplasm,  the  living  cell-substance  of  both  animals  and 
plants.     The  carbohydrates,  such  as  the  starch-granules  or 
the  sugar  of  any  vegetable  cell,  form  a  large  portion  of  its 
food,  while  fats  are  eaten  probably  in  small  quantities. 

The  digestive  fluid  of  the  earthworm  resembles  the  digest- 
ive fluid  of  the  higher  animals,  not  only  in  being  capable  of 
acting  on  the  three  important  classes  of  organic  foods,  but  also 
in  containing  some  of  the  same  special  chemical  compounds 


THE  EARTHWORM 


199 


which  have  the  digestive  action.  These  are  called  ferments,  or 
enzymes.  The  peculiar  quality  of  an  enzyme  is  to  cause  a 
chemical  change  in  another  substance  without  itself  losing 
any  of  its  own  properties.  Thus,  trypsin,  the  enzyme  which 
acts  on  proteids,  can  do  so  and  still  remain  trypsin.  Similarly, 
the  enzyme  diastase  acts  upon  starch,  and  steapsin  upon  fats. 

Let  us  consider  for  a  moment  why 
it  is  necessary  for  the  earthworm, 
or  any  animal,  to  secrete  elaborate 
chemical  mixtures  like  digestive 
fluids.  If  we  were  to  examine  the 
alimentary  canal  of  the  earthworm, 
we  should  find  that  there  are  no 
openings  leading  from  the  canal  to 
the  body-cavity  which  might  permit 
food  to  pass  directly  to  different 
organs.  The  wall  of  the  canal  is 
thin,  but  it  is  made  of  cells  which 
are  packed  closely  together.  Water 
will  pass  through  this  membrane 
easily,  but  certain  other  substances, 
although  in  a  liquid  state,  will  not 
pass  through  so  readily.  Those  solu- 

f.  ,.?  j.1         '     u  •        i 

tions  which  pass  through  an  animal- 
membrane  readily  are  called  crystal- 

7    .  ,        ,.  ,  r>      i 

loids;  for  example,  solutions  of  salt  or 
sugar.  Liquids  which  do  not  pass  readily  through  an  animal- 
membrane  are  known  as  colloids;  for  example,  solutions  of 
meat-juice  or  starch.  The  action  of  the  digestive  fluid  is  a 
double  one  :  it  changes  the  state  of  the  solid  food  physically, 
by  rendering  it  liquid  ;  it  changes  the  state  of  organic  foods 
'(both  solid  and  liquid)  chemically,  giving  at  the  same  time  to 
each  of  the  altered  food-substances  a  new  physical  property, 
namely,  that  of  being  able  to  pass  through  the  intestine-wall. 


i«-  101.  Experiment  show- 
ing  Osmosis 

»  bottle;  2,  water;  3,  tube; 

4>  piece  of  sheep,s  intestine 
containing  salt-solution; 

5,  level  of  salt-solution 


200  GENERAL  ZOOLOGY 

For  illustration,  we  may  suppose  that  an  earthworm  has 
swallowed  a  small  piece  of  potato  which  contains  a  great  deal 
of  starch.  In  the  intestine  the  starch  is  changed  physically  by 
being  made  liquid  or  partially  so,  and  it  is  changed  chemically 
by  the  enzyme  diastase  into  a  sugar-compound.  In  the  latter 
state,  what  was  once  starch  passes  readily  through  the  wall  of 
the  intestine.  A  proteid  substance  like  iVeat-juice  cannot  pass, 
except  in  a  slight  degree,  through  the  intestine  until  it  has 
been  changed  chemically ;  this  is  done  by  the  enzyme  trypsin. 
The  changed  substance  is  called  a  peptone.  It  is  not  likely 
that  earthworms  in  nature  ever  need  to  digest  considerable 
quantities  of  fat,  but  in  experiments  fats  have  been  fed  to 
earthworms.  Results  followed  similar  to  those  obtained  in 
many  other  animals  which  usually  consume  fats.  The  enzyme 
steapsiri  separates  the  fats  into  compounds  known  as  glycerin 
and  fatty  acid.  The  fatty  acids  combine  chemically  with  the 
alkali  in  the  digestive  tract,  resulting  in  compounds  similar 
to  soap ;  the  process  is  therefore  called  saponification.  When 
the  proteids  are  changed  to  peptones,  the  starch  to  sugar,  and 
the  fats  to  glycerin  and  soaps,  then  these  organic  foods  are 
ready  to  pass  with  any  inorganic  foods,  —  as,  for  example, 
salt  and  water,  —  through  the'  wall  of  the  intestine. 

Absorption.  Digested  food  passes  through  the  intestine- 
wall  and  mixes  with  the  body-fluids,  in  accordance  with  a 
principle  known  in  physics  as  osmosis  (see  Fig.  101).  In  the 
experiment  illustrated  in  the  figure  there  is  a  salt-solution 
in  the  sac  made  of  sheep's  intestine  (Fig.  101,  4),  and  pure 
water  in  the  beaker  outside.  The  experiment  is  supposed 
to  have  been  started  with  the  salt  water  and  the  pure  water 
at  the  same  level.  Within  a  half-hour  the  level  of  the  salt- 
solution  has  risen  several  inches.  Besides,  some  of  the  salt- 
solution  has  passed  through  the  membrane  into  the  pure  water. 
It  is  one  of  the  phenomena  of  osmosis  that  a  greater  amount 
^of  liquid  passes  from  the  less  dense  to  the  more  dense  solution 


THE  EARTHWORM  201 

than  in  the  contrary  direction.  If  the  pure  water  in  the  ex- 
periment were  replaced  by  a  colloid-solution,  then  the  pas- 
sage of  liquid  would  practically  all  be  from  the  salt-solution 
into  the  colloid-solution. 

It  is  well  known  that  a  crystalloid,  like  salt  or  sugar,  if 
placed  in  a  vessel  of  water,  will  soon  diffuse  through  the  water. 
In  doing  so  it  exerts  a  certain  amount  of  pressure.  This  is 
called  osmotic  pressure.  If  a  permeable  membrane  be  inter- 
posed between  a  solution  of  crystalloids  and  one  of  colloids, 
both  substances  will  exert  some  osmotic  pressure,  but  by 
far  the  greater  amount  is  exerted  by  the  crystalloid,  because 
of  its  greater  facility  in  diffusing  through  water.  Applying 
the  principle  of  osmosis  to  absorption  in  the  intestine  cf  the 
earthworm,  we.  have  crystalloids  in  the  cavity  of  the  intes- 
tine, a  permeable  though  not  porous  membrane  (the  intestine- 
wall),  and  colloids  in  the  blood  and  body-cavity  fluid.  The 
digested  food  diffuses  through  the  intestine-wall  because  of 
the  pressure  it  exerts  in  seeking  to  mix  with  more  water. 
Food  on  passing  to  the  blood  is  changed  by  the  cells  of 
the  intestine-wall  from  the  crystalloid  condition  to  a  col- 
loid, and  is  henceforth  incapable  of  passing  back  through  the 
membrane. 

Circulation.  Whenever  an  animal  body  is  too  large  or  com- 
plicated for  the  food  to  reach  all  the  cells  directly,  we  find 
a  circulatory  system  developed.  The  circulatory  system  of 
the  earthworm  is  complete,  and  rather  complex.  The  dor- 
sal blood-vessel  (Fig.  100,  17)  extends  the  length  of  the  animal, 
along  the  middle,  between  the  body- wall  and  the  alimentary 
canal.  The  blood  flows  toward  the  anterior  region  in  some- 
what regular  "  pulses,"  carried  along  by  waves  of  muscular 
contraction  in  the  wall  of  the  blood-vessel  itself.  Between 
the  pharynx  and  the  crop  are  situated  five  pairs  of  "hearts" 
(Fig.  100,  19,  20).  These  short  tubes  receive  most  of  the 
blood  that  comes  forward,  take  up  the  waves  of  contraction- 


202  GENERAL  ZOOLOGY 

sent  along  the  dorsal  vessel,  and  force  the  'blood  into  theJ 
ventral  blood-vessel  (Fig.  100,  22),  which  carries  it  posteriorly 
in  a  regular  flow.  Below  the  ventral  nerve-chain  is  the  sub- 
neural  blood-vessel  (Fig.  100,  23),  in  which  the  blood  prob- 
ably flows  backward.  The  lateral  blood-vessel  (Fig.  100,  21), 
with  its  connections,  is  limited  to  the  region  anterior  to  the 
crop.  Capillaries  (fine  blood-vessels  joining  larger  ones)  branch 
in  the  wall  of  the  intestine  and  connect  in  a  very  complicated 
fashion  with  all  the  large  vessels.  Absorbed  food  passes  into 
the  capillaries  and  is  carried  with  the  blood  to  the  larger 
blood-vessels,  to  be  transported  to  all  parts  of  the  body.  All 
about  the  intestine,  in  the  hollow  spaces  of  the  somites,  tliei 
is  a  large  quantity  of  body-cavity  fluid,  which  is  very  much 
like  the  blood  in  the  vessels,  except  that  it  is  colorless.  It  is 
thought  that  much  of  the  absorbed  food  mixes  with  this 
fluid.  The  outcome  is  the  same  with  food  carried  by  the  regu- 
lar circulatory  system  and  with  that  taken  up  by  the  bod}-- 
cavity  fluid. 

Assimilation.    The  food  is  transported  by  the  blood  in  the 
blood-vessels  or  in  the  bodj^-cavity  to  tissues,  where  some  of 
it  is  transformed  into  protoplasm.    Just  how  this  is  done  no 
one  has  been  able  to  discover,  but  it  is  known  that  the  trans- 
forming process,  which  is  called  assimilation,  takes  place  in 
tissues  which  are  alive, — for  example,  muscles  and  nerves. 
We  know  that  the  building  up  of  new  protoplasm  takes  plac 
in  growth,  when  new  cells  are  formed,  and  that  it  is  also  made 
necessary  on  account  of  the  slow  and  imperceptible  destriu. 
tion  of  the  protoplasm  in  oxidation  (see  below). 

It  will  be  helpful  at  this  point  to  know  that  of  all  the  food 
taken  into  the  circulatory  system  of  an  animal  but  very  little 
except  during  growth,  is  actually  made  into  protoplasm.^ 
The  carbohydrates  and  the  fats  that  are  absorbed,  aiid  those 
that  are  made  from  proteids  by  the  protoplasm,  together  with 
some  unassimilated  proteids,  are  destroyed  after  they  have 


THE  EARTHWORM  203 

been  stored  temporarily  either  in  the  lining  of  the  body- 
cavity,  in  the  muscle-cells,  or  in  the  fat-cells.  Protoplasm 
itself  breaks  down,  but  to  a  less  extent. 

First  Stage  of  Respiration.  The  earthworm  has  neither  gills, 
tracheae,  nor  lungs;  still  it  can  breathe  quite  as  perfectly  as  the 
animals  which  possess  one  or  another  of  those  organs.  The 
essential  characteristic  of  a  breathing  organ  is  a  thin,  moist 
membrane,  with  thin-walled  capillary  blood-vessels  on  one  side 
and  air  on  the  other.  The  outer  skin  of  the  earthworm  is 
thin  and  moist,  and  just  beneath  it  are  capillaries.  While  in 
its  burrow,  or  even  in  water,  air  comes  in  contact  with  the 
skin,  and  its  most  important  element,  oxygen,  passes  through 
and  mixes  with  the  blood.  The  second  stage  of  respiration 
comes  after  oxidation,  in  the  series  of  events  here  described. 

Oxidation.  In  the  circulating  blood  there  is  a  red-colored 
Mibstance  called  haemoglobin.  Oxygen  combines  chemically 
with  this,  and  the  compound  goes  with  the  blood  until  it 
reaches  tissue-cells  which  have  some  food  stored  in  them; 
then  the  oxygen  combines  with  the  food,  which  may  be  car- 
bohydrate, fat,  or  proteid.  The  chemical  union  of  oxygen 
with  other  elements  is  of  the  greatest  importance  in  the  life 
of  any  plant  or  animal.  A  simple  example  of  the  result  of 
the  chemical  union  of  oxygen  with  another  element  may  be 
observed  in  the  burning  of  coal.  It  is  well  known  that  coal 
is  composed  chiefly  of  carbon.  When  a  quantity  of  coal  is 
heated  it  begins  to  unite  with  oxygen  from  the  air.  During 
this  process  four  phenomena  may  be  observed :  first,  the  quan- 
tity of  oxygen  in  the  room  is  reduced ;  second,  the  quantity 
of  coal  is  reduced ;  third,  an  invisible  gas  is  formed ;  and 
fourth,  heat  and  light  are  given  off. 

When  oxygen  unites  chemically  with  carbon  two  kinds  of 
gas  may  be  formed,  either  carbon  monoxide  or  carbon  dioxide, 
or  both.  The  union  of  a  solid  element  with  a  gaseous  one 
to  form  a  gaseous  compound  accounts  for  the  fact  that  so 


204  GENERAL  ZOOLOGY 

great  a  mass  of  coal  disappears  in  burning,  leaving  only  the 
mineral  ash  behind.  We  call  the  union  of  oxygen  with  an- 
other element  oxidation. 

Forms  of  Energy.  It  is  important  to  observe  that  as  oxi- 
dation takes  place  heat  and  light,  which  are  called  forms  of 
energy,  are  given  off.  Energy  —  that  is,  the  power  to  do  work 
—  can  be  transformed  from  one  form  to  another ;  for  example, 
the  heat  derived  by  oxidizing  coal  may  be  transformed  into 
mechanical  energy  like  that  of  an  engine,  and  the  mechanical 
energy  may  be  changed  into  electricity,  and  the  electricity 
into  mechanical  energy  again,  or  into  heat  and  light.  We 
may  regard  the  energy  which  is  suddenly  released  upon  the 
oxidation  of  the  carbon  in  the  coal  as  having  been  stored  there 
by  the  sun  millions  of  years  ago,  when  the  coal  was  the  grow- 
ing tissue  of  a  tree.  We  may  borrow  from  physics  two  other 
terms  which  will  help  us  in  getting  the  notion  of  the  states  in 
which  energy  may  exist.  Energy  at  rest  —  as,  for  example, 
chemical  affinity  (that  is,  the  readiness  of  the  carbon  to  com- 
bine with  oxygen)  —  is  called  potential  energy ;  energy  in  action, 
as  heat,  light,  electricity,  and  motion,  is  called  kinetic  energy. 
As  we  have  already  seen,  potential  energy  may  become  kinetic 
energy,  and  kinetic  energy  may  become  potential  energy. 

When  the  earthworm  swallows  a  bit  of  leaf  which  passes 
through  all  stages  of  digestion,  absorption,  circulation,  and 
food-storing,  or  assimilation,  the  form  of  the  bit  of  leaf  is 
completely  lost,  and  the  chemical  composition  is  also  changed ; 
but  oxidation  has  not  taken  place,  and  hence  the  potential 
energy  transformed  from  the  kinetic  energy  of  the  sun  (heat 
and  light)  when  the  leaf  grew,  remains  unchanged  until  the 
all-important  phenomenon  of  oxidation  occurs. 

Carbohydrates,  and  especially  fats,  are  capable  of  combin- 
ing with  a  relatively  large  amount  of  oxygen,  because  of  the 
small  proportion  of  that  element  in  those  compounds,  and  the 
large  proportion  of  carbon.  Carbohydrates,  chiefly  glycogen, 


THE  EARTHWORM  205 

one  of  the  many  kinds  of  sugar  in  nature,  are  frequently  made 
from  proteids  by  the  protoplasm  in  the  cells,  and  are  stored 
in  the  liver-cells  of  the  higher  animals,  to  be  later  transported 
to  their  muscle-cells  and  stored  in  them  until  needed.  In 
animals  that  have  no  liver,  as  the  earthworm,  the  glycogen 
is  stored  in  the  cells  of  the  lining  of  the  body-cavity,  and  in 
the  muscles.  A  French  physiologist,  Chauveau,  believes  that 
"the  glycogen  incorporated  in  the  muscular  tissue  puts  at 
the  service  of  the  tissue  the  energy  which  it  needs  for  its 
work."  This  theory  is  valuable,  because  it  enables  us  to  see 
how  the  energy  (heat)  released  by  the  oxidation  of  the  small 
particles  of  glycogen  in  the  muscle-cells  may  be  transformed 
into  muscular  energy  without  loss.  Fats,  made  either  from 
carbohydrates  or  from  proteid  food  by  the  protoplasm,  or 
stored  directly  in  cells  from  the  fatty  acids  absorbed  through 
the  intestine,  are  reserve  material,  and  are  capable  of  supply- 
ing energy  when  there  is  need  of  it. 

Second  Stage  of  Respiration.  When  carbohydrates  and  fats 
are  oxidized  the  resulting  compounds  are  carbon  dioxide  and 
water,  as  these  foods  contain  only  carbon,  hydrogen,  and 
oxygen.  Proteids  are  far  more  complex.  All  proteids  con- 
tain at  least  carbon,  hydrogen,  nitrogen,  oxygen,  sulphur,  and 
usually,  in  addition,  phosphorus.  When  they  are  oxidized 
many  different  compounds  result.  The  best  known  of  these 
are  uric  acid,  carbon  dioxide,  and  water.  All  these  com- 
pounds are  wastes.  Carbon  dioxide,  whether  derived  from 
carbohydrates,  fats,  or  proteids,  makes  its  way  by  the  blood 
to  the  skin-capillaries  of  the  earthworm,  and  there  passes 
through  the  moist  membrane  to  the  air  outside.  The  first 
stage  of  respiration  consists  of  the  absorption  of  oxygen  by 
the  blood-vessels  of  the  skin  ;  the  second  stage  is  the  excre- 
tion of  carbon  dioxide  from  the  same  blood-vessels,  through 
the  skin.  The  entire  process  of  respiration  consists  simply 
of  an  exchange  of  gases  through  a  membrane. 


206  GENERAL  ZOOLOGY 

Metabolism.  Before  discussing  the  last  of  the  series  of 
physiological  processes,  it  will  prove  helpful  to  consider  all 
that  has  been  said  as  being  descriptive  of  processes  that  are 
merely  stages  of  the  one  great  sum-process  of  living.  In 
scientific  terminology  we  call  this  sum-process  metabolism. 
Considered  as  a  single  process,  we  recognize  a  series  of  events 
during  which  things  are  coming  into  the  body.  These  things 
are  in  the  course  of  making  up  a  part  of  the  body  of  the 
organism ;  this  is  called  constructive  metabolism,  anabolic 
metabolism,  or  simply  anabolism  (Gr.  ana,  up ;  ballein,  to 
throw).  Upon  the  occurrence  of  oxidation,  food  stored  in 
the  muscle-cells,  and  protoplasm,  when  it  is  oxidized,  are 
broken  up  and  reduced  to  simpler  chemical  compounds  ; 
this  is  destructive  metabolism,  katabolic  metabolism,  or  katab- 
olism  (Gr.  kata,  down ;  ballein,  to  throw).  The  products  of 
katabolic  metabolism  are  the  wastes  of  the  organism.  The 
undigested  food  and  the  indigestible  substances  that  pass 
through  the  length  of  the  intestine  are  not  considered 
wastes,  —  a  fact  that  has  already  been  stated  in  the  chapter 
on  the  locust. 

Excretion.  The  last  of  the  stages  of  metabolism  is  excre- 
tion. In  the  broadest  sense  of  the  term  excretion  includes 
all  those  activities  which  result  in  ridding  the  body  of  wastes. 
Carbon  dioxide  is  given  off  only  from  the  skin ;  water  prob- 
ably in  part  from  the  skin ;  uric  acid  and  water  are  discharged 
from  pairs  of  small  contorted  funnel-shaped  tubes  in  the  lateral 
portions  of  the  cavity  of  the  somites  of  the  earthworm.  These 
excretory  organs  are  called  nephridia  (Fig.  100,  25,  26).  They 
correspond  in  function  to  the  kidneys  of  the  higher  animals. 
Each  nephridium  has  the  mouth  of  its  funnel  extending 
through  a  septum  (Fig.  100,  4)  into  the  cavity  immediately 
anterior  to  the  somite  which  contains  the  greater  portion  of 
the  organ.  The  external  opening  of  a  nephridium  is  on  the 
ventral  surface. 


THE  EARTHWORM  207 

The  funnel-shaped  end  of  a  nephridium  is  provided  with 
cilia  (hair-like  structures)  inside,  which  wave  downward  and 
carry  out  such  liquid  waste  products  as  collect  in  the  body- 
cavity.  Blood-vessels,  which  break  up  into  capillaries  in  the 
wall  of  the  nephridium,  also  carry  a  certain  amount  of  waste. 
The  excess  water  and  the  nitrogenous  waste  in  the  blood 
are  separated  in  these  capillaries  ancTgo  down  the  tube,  to 
be  discharged  at  the  external  opening.  The  body-cavity  fluid 
is  filled  with  small,  free-moving  cells,  called  amoebocytes. 
They  have  the  power  of  changing  their  form  quickly  by 
extending  irregular  pointed  processes  from  any  part  of  the 
cell-body.  Owing  to  this  power  they  can  inclose  any  small 
particle  of  solid  matter.  The  amcebocytes  dissolve  solid  par- 
ticles that  fall  from  the  superficial  cells  of  the  intestine. 
Frequently  they  make  their  way  through  the  entire  intestine- 
wall,  and  are  passed  to  the  exterior  with  the  contents  of  the 
alimentary  canal,  carrying  the  waste  products  with  them. 

Nerve  Control.  In  the  preceding  paragraphs  we  have  been 
considering  the  stages  of  metabolism,  without  making  any 
reference  to  the  fact  that  no  activity  of  internal  or  external 
organs  could  take  place  in  the  body  of  the  earthworm  if  it 
were  not  for  the  controlling  influence  of  the  nervous  system. 
Ingestion,  digestion,  absorption,  circulation,  respiration,  oxi- 
dation, and  excretion  constitute  a  chain  of  processes,  largely 
because  the  nervous  system,  acting  through  the  system  of 
muscles,  especially  in  the  digestive  and  the  circulatory  sys- 
tems, causes  them  to  take  place  according  to  a  definite  plan. 
In  order  to  understand  how  the  nervous  system  of  the  earth- 
worm may  act,  it  will  be  necessary  first  to  have  some  knowl- 
edge of  the  structure  of  its  nervous  tissue. 

The  general  plan  of  the  nervous  system  of  the  earthworm 
is  similar  to  that  of  the  locust  and  the  crayfish,  but  Less 
specialization  is  evident  than  in  either  of  the  other  animals. 
The  " brain"  (supraoesophageal  ganglion,  Fig.  100,  27)  is  a 


208  GENERAL  ZOOLOGY 

simple,  very  small,  bilobed  ganglion,  joined  by  connectives 
to  a  suboesophageal  ganglion  (Fig.  100,  28) ;  from  the  latter  a 
pair  of  connectives  extend  along  the  ventral  wall  of  the  body- 
cavity  to  the  posterior  end,  with  a  ganglion  (Fig.  100,  29)  at 
every  somite.  The  brain  and  ventral  nerve-chain  constitute 
the  central  nervous  system.  From  each  ganglion  of  the  ven- 
tral chain  two  pairs  of  nerves  run  out  to  the  muscles  of  the 
body-wall  and  the  internal  organs,  and  one  pair  begins  in 
the  connective  near  by.  The  entire  set  of  nerves  leaving  the 
central  nervous  system  constitutes  the  peripheral  (surface) 
nervous  system. 

If  we  were  to  trace  one  of  the  nerves  outward  from  the  cen- 
tral nervous  system  as  it  penetrates  the  muscular  tissue,  we 
should  find  that  it  divides  into  many  very  fine  fibers.  Certain 
fibers  can  be  traced  to  the  end  as  they  merge  their  substance 
with  a  muscle-fiber.  The  nerve-fiber  that  is  united  to  a 
muscle-fiber  (Fig.  102,  9)  is  a  slender  portion  of  a  nerve-cell 
(Fig.  102,  8),  the  nucleus  (Fig.  102,  7)  of  which  is  in  the 
central  nervous  system  (Fig.  102,  6).  Nerve-cells  of  this  t}^pe 
are  called  motor  nerve-cells.  The  fibers  of  many  motor  nerve- 
cells  lie  parallel  in  every  nerve.  ' Mingled  with  them  is 
another  type  of  nerve-cell  which  has  its  nucleus  (Fig.  102,2) 
at  or  near  the  skin  of  the  animal,  and  the  terminal  portion  of 
its  principal  fiber  (Fig.  102,  3,  4,  5)  extending  into  the  central 
nervous  system.  Cells  of  this  type  are  called  sensory  nerve-cells. 

Reflex  Action.  In  case  an  object  touches  one  of  the  fine 
sensory  hairs  on  the  skin  (Fig.  102,  l)  of  an  earthworm,  a 
nervous  impulse  is  sent  along  the  sensory  fiber  to  the  ventral 
nerve-chain.  There  the  impulse  is  transferred  to  the  short 
branches  of  motor  fibers,  and  by  them  ultimately  to  the  prin- 
cipal motor  fiber  (Fig.  102,  8).  When  the  impulse  reaches 
the  end  of  the  nerve-fiber,  the  muscle-fiber  (Fig.  102,  9)  to 
which  it  is  attached  contracts.  When  many  sensory  nerve- 
cells  are  stimulated  in  this  way,  many  motor  cells  will  carry 


THE  EARTHWORM 


209 


out  the  transferred  impulse,  the  muscles  will  contract,  and 
the  animal  moves  away.  This  kind  of  nerve-action  is  called 
reflex  action  because,  in  a  sense,  the  impulse  is  reflected  back 
from  the  ventral  nerve-chain. 
Reproduction.  Every  earth- 
worm contains  both  spermaries 
and  ovaries.  As  explained  on 
page  176,  animals  which  have 
the  male  and  female  glands  in 
the  same  body  are  called  her- 
maphrodites. There  are  two 
pairs  of  spermaries  in  the  earth- 
worm hidden  by  the  three  pairs 
of  seminal  vesicles^indic'dted  in 
Fig.  100,  30, 31.  The  single  pair 
of  ovaries  (Fig.  100,  35)  is  very 
small.  Although  each  earth- 
worm produces  spermatozoa 
and  eggs,  the  eggs  of  one  indi- 
vidual are  always  fertilized  by 
the  spermatozoa  of  another. 
During  the  breeding  season, 
which  extends  through  the 
greater  part  of  the  year,  earth- 
worms occasionally  meet  be- 
neath stones  and  logs,  and  affix 
the  ventral  surfaces  of  their 
bodies  together  by  the  anterior 
thirds  pointed  in  opposite  directions,  and  each  expels  a  quan- 
tity of  its  spermatozoa  which,  are  received  in  cavities  of  the 
other,  opening  from  the  outside.  These  cavities  (seminal 
receptacles)  are  four  in  number,  and  are  in  the  ninth  and  tenth 
somites  (Fig.  100,  33,  34).  They  retain  the  spermatozoa  until 
the  eggs  are  ready  to  be  laid. 


FIG.  102.  Reflex  Action  in  the  Earth- 
worm. (Reconstructed  from 
drawings  by  Havet) 

(The  arrows  indicate  the  path  of  the  ner- 
vous impulse) 

1,  cuticle  of  skin  ;  2,  sensory  nerve- 
ganglion  ;  .'$,  sensory  nerve-fiber ; 
4,  anterior  branch  of  sensory  nerve- 
fiber  ;  5,  posterior  branch  of  sensory 
nerve-fiber ;  6,  ventral  nerve-cord  ; 
7,  motor  nerve-ganglion ;  8,  motor 
nerve-fiber;  9,  longitudinal  muscle- 
fibers 


210 


GENERAL  ZOOLOGY 


The  presence  of  the  thick  band,  the  clitellum  referred  to  on 
page  196,  indicates  that  the  individual  is  sexually  mature. 
The  clitellum  is  provided  with  glands  on  its  ventral  surface. 
Just  preceding  the  time  of  egg-laying  these  glands  secrete 
a  thick  mucus  which  forms  a  ring  about  the  clitellum.  Into 
the  space  between  this  ring  and  the  body  is  poured  a  milky 
secretion  which  is  food  for  the  young  earthworms.  The  ring  of 
mucus  is  then  moved  forward  slowly.  At  the  fourteenth  somite 
the  eggs  are  caught  up  from  the  oviduct  (Fig.  100,  36),  which 


ov 


A  B  C 

FIG.  103.  Egg-capsule,  Egg,  and  Spermatozoon,  of  Earthworm 

A,  egg-capsule.    B,  egg  with  nucleus:  ov,  eggs,  about  natural  size.    C,  spermato- 
zoon: n,  nucleus;  w,  middle  piece;  t,  tail 

(From  Sedgwick  and  Wilson's  General  Biology) 

forces  them  out,  at  the  time  the  ring  passes.  Farther  forward 
the  spermatozoa  that  have  been  stored  in  the  seminal  recepta- 
cles are  received  into  the  ring,  and  while  the  ring  is  making 
its  way  forward,  fertilization,  which  consists  of  the  union  of 
the  spermatozoon  with  the  egg,  takes  place.  At  the  anterior 
end  the  ring  begins  to  draw  together  at  the  ends,  and  when 
this  egg-capsule  (Fig.  103,  A)  has  been  pushed  off,  it  is  a  short, 
spindle-shaped,  tough-coated  sac,  about  as  large  as  a  grain  of 
wheat,  inside  of  which  all  the  eggs  are  fertilized.  Few  of  them, 
however,  reach  the  stage  of  young,  free-moving  earthworms. 


THE  EARTHWORM  211 

Egg-capsules  are  found  buried  in  the  soil  and  under  stones 
and  boards  and  other  protected  places.  They  are  often  mis- 
taken for  seeds  of  some  plant,  which  accounts  for  their  iden- 
tity being  unknown  to  most  people. 

From  the  drawing  we  get  an  idea  of  the  relative  size  of 
the  egg  (Fig.  103,  B)  and  the  spermatozoon  (Fig.  103,  C).  In 
the  case  of  animals  which  produce  a  large,  yolk-filled  egg, 
e.g.  birds,  the  difference  in  size  between  the  egg  and  sper- 
matozoon is  far  greater.  The  spermatozoon  of  all  animals  is 
microscopic  in  size. 

Maturation.  The  phenomena  of  fertilization  in  the  egg  of 
the  earthworm  are  not  so  well  known  as  they  are  in  a  near 
relative,  the  sandworm,  Ne'reis  (Fig.  107).  The  series  of  fig- 
ures (Fig.  104,  J,  /?,  C,  D,  E,  F,  maturation  or  egg-ripening 
in  Nereis)  illustrates  in  a  general  way  the  phases  through 
which  the  eggs  of  animals  pass  before  they  begin  to  develop. 
Fig.  104,  A  shows  the  egg  fully  grown  and  ready  to  receive 
the  spermatozoon.  Among  the  things  to  be  noted  are  the 
egg-membrane  and  the  nucleus  containing  the  germinal  spot. 
Imbedded  in  the  fine  granular  protoplasm  (cytoplasm)  about 
the  nucleus  are  the  yolk-granules,  destined  to  nourish  the 
developing  embryo,  and  some  large  fat-globules. 

At  about  the  time  of  penetration  of  the  egg  by  the  sper- 
matozoon (Fig.  104,  B)  the  egg-nucleus  begins  to  lose  its  out- 
Une  because  of  the  encroachment  of  a  spindle-shaped  structure 
^ormetl  from  minute  fibers  in  the  cytoplasm.  At  either  pole 
of  the  spindle  is  an  extremely  small  granule.  These  are 
illed  centrosomes  (central  bodies).  They  appear  to  dominate 
the  formation  of  the  spindle  and  its  movements  after  forma- 
tion. The  spindle  draws  from  the  egg-nucleus  a  definite 
number  of  small,  rod-like  bodies  called  chromosomes  (colored 
odies).  They  are  so  called  because  in  preparations  of  thin 
ices  of  the  egg  these  little  bodies  stain  in  certain  dyes  more 
b  illiantly  than  any  other  part. 


FIG.  104.  Maturation  and  Fertilization  in  Nereis 

A,  egg  with  germinal  spot;  B,  egg  with  first  spindle  forming,  sperm-cell  small ; 
C,  egg  with  first  spindle  at  periphery,  two  sperm-centrosomes ;  I),  egg  with 
one  polar  cell  formed,  spindle  with  sperm-cell ;  E,  egg  with  second  polar  cell 
formed,  spindle  from  sperm-centrosomes ;  f,  first  cleavage  spindle,  first 
stage  of  embryo 

(From  Wilson's  The  Cell) 
212 


THE  EARTHWORM  213 

After  the  chromosomes  are  arranged  across  the  middle  of 
the  spindle,  the  entire  spindle  moves  end  on  toward  the  sur- 
face of  the  egg.  As  it  does  so  the  chromosomes  divide  each 
into  halves  and  are  drawn  to  the  poles  (Fig.  104,  C).  The 
outer  pole  makes  a  prominence  on  the  cell-wall,  and  soon  a 
little  body  is  formed,  the  spindle  dividing  across  the  middle. 
We  'observe  that  this  little  body  is  really  a  cell,  because  it 
has  a  nucleus  with  chromosomes,  a  little  cytoplasm,  and  a 
wall  about  it.  It  is  called  the  first  polar  cell.  That  portion 
of  the  spindle  which  was  left  in  the  egg  disappears,  but  the 
little  centrosome  still  exists.  It  soon  divides  into  two,  and 
the  parts,  gradually  separating,  form  a  spindle  between  them. 
The  chromosomes  are  again  arranged  on  the  spindle.  Then 
the  spindle  (Fig.  104,  D)  swings  around  into  the  plane  of 
the  first  spindle.  As  the  spindle  moves  toward  the  cell-wall 
again  the  chromosomes  divide  as  before.  A  second  polar  cell 
is  formed  beneath  or  slightly  to  one  side  of  the  first.  The 
process  of  maturation  is  completed  by  this  phase. 

Fertilization.  In  the  eggs  of  many  animals  the  entrance 
of  the  spermatozoon  appears  to  be  a  stimulus  for  the  begin- 
ning of  maturation.  Whether  the  spermatozoon  enters  before 
or  after  maturation  has  begun,  it  cannot  take  part  in  the 
process  of  development  until  the  second  polar  cell  has  been 
formed.  When  this  has  taken  place  in  Nereis,  the  egg-spindle 
and  the  egg-centrosomes  both  disappear,  leaving  the  egg- 
chromosomes  inclosed  in  a  nuclear  membrane. 

The  spermatozoon  on  entering  the  egg  leaves  the  "  tail " 
outside,  its  locomotor  function  being  at  an  end.  The  "head," 
which  is  really  the  nucleus  of  the  spermatozoon-cell,  or  sperm- 
cell  as  we  may  now  call  it,  becomes  rounded  and  for  a  time 
remains  quiescent  (Fig.  104,  B).  As  indicated  in  Fig.  104,  C, 
the  sperm-cell  becomes  larger,  and  is  drawn  toward  the  cen- 
tral region  of  the  egg  by  a  centrosome,  which  we  shall 
call  the  sperm-centrosome,  because  it  came  into  the  egg  with 


214  GENERAL  ZOOLOGY 

the  sperm-nucleus.  As  the  sperm-centrosome  with  its  sperm- 
aster  (star-like  arrangement  of  egg-cytoplasm  fibers)  is  draw- 
ing the  sperm-nucleus  inward,  division  of  the  centrosome 
takes  place  and  a  spindle  begins  to  form  (Fig.  104,  D).  At 
the  same  time  the  sperm-nucleus  enlarges  to  the  size  of  an 
egg-nucleus.  The  new  spindle  with  its  enlarged  sperm- 
nucleus  moves  forward  until  it  comes  in  contact  with  the 
egg-nucleus  (Fig.  104,  j£),  which  we  remember  has  lost  its 
centrosome  and  spindle. 

The  fibers  of  the  spindle  penetrate  the  nuclear  membranes 
of  both  egg-nucleus  and  sperm-nucleus,  and  drag  into  the 
middle  plane  of  the  spindle  all  the  chromosomes,  the  same  num- 
ber from  each  nucleus.  By  this  act  fertilization  is  completed, 
and  the  new  individual  begins  its  existence  as  an  embryo. 

Development.  The  spindle  that  is  formed  at  the  comple- 
tion of  fertilization  is  called  the  cleavage  spindle.  After  the 
chromosomes  divide  (Fig.  104,  7'1),  and  are  drawn  toward 
either  pole,  the  young  embryo  cleaves  or  divides  through  the 
middle,  so  that  in  each  cell  there  is  an  equal  amount  of  cyto- 
plasm. There  is  also  in  each  cell  a  nucleus  containing  chro- 
mosomes, half  of  which  came  from  the  egg-nucleus  and  half 
from  the  sperm-nucleus.  Each  of  the  two  cells  divides  again, 
making  four  cells.  The  polar  cells  disappear  after  a  time. 

In  the  eight-cell  stage  in  the  earthworm  there  is  the  begin- 
ning of  a  cavity  at  the  center  of  the  small  sphere.  As  the 
number  of  cells  increases  the  cavity  becomes  relatively  larger, 
although  the  diameter  of  the  hollow  sphere 'is  no  greater  than 
the  diameter  of  an  unfertilized  egg.  When  the  cavity  reaches 
its  maximum  relative  size  the  cells  are  arranged  in  a  single 
layer  just  beneath  the  original  egg-membrane.  This  is  called 
the  blastula  stage.  In  this  stage,  as  seen  in  Fig.  105,  B,  a  sec- 
tion through  the  blastula  shows  that  the  upper  cells  are  smaller 
than  the  lower  cells.  The  larger  cells  flatten  and  soon  begin 
to  bend  inward,  as  shown  in  Fig.  105,  D.  The  effect  of  this 


THE  EARTHWORM 


215 


is  to  decrease  the  blastula  cavity  and  to  make  another  cavity 
with  a  wide  opening  to  the  outside  (Fig.  105,  _#,  F).  This  is 
the  gastnda  (little  stomach)  stage.  It  is  appropriately  called 
so,  because  at  this  time  the  embryo  first  begins  to  take  food 
in  the  egg-capsule ;  the  food  is  digested  in  the  cavity  formed 
from  the  outside.  In  the  gastrula  it  is  possible  to  distinguish 
two  layers  of  cells,  both  of  which  we  know  came  originally 


E 

FIG.  105.    Early  Stages  of  Development  of  Earthworm.    Much  enlarged 

A,  blastula,  surface  view.  B,  blastula,  section:  s.c.,  blastula  cavity ;  m,  first  cell 
of  mesoderm.  C,  blastula,  later  stage.  D,  blastula,  flattening  of  future 
endodermal  cells.  E,  gastrula,  in  side  view :  ec,  ectoderm ;  en,  endoderm ; 
s-s,  line  of  section  for  F.  F,  gastrula,  cross  section :  ar,  archenteron 

(From  Sedgwick  and  Wilson's  General  Biology) 

from  a   single   layer;   -these  two   layers  are   called  ectoderm 
(Fig.  105,  E,  ec)  and  endoderm  (Fig.  .105,  E,  en). 

While  the  embryo  is  still  in  the  blastula  stage  a  single  cell 
(Fig.  105,  B,  m)  can  be  identified  as  one  which  later  develops 
into  a  row  of  cells  on  either  side,  and  finally  into  a  mass  of 
tissue  on  either  side,  to  which  we  give  the  name  mesoderm 
(Fig.  105,  F).  Many  animals  pass  through  these  stages  ;  hence 
the  use  of  the  terms  ectoderm,  endoderm,  and  mesoderm,  as 


216  GENERAL  ZOOLOGY 

the  primary  germ-layers,  has  very  great  significance.  Already 
we  can  note  many  changes  from  the  simple  blastula  condition 
to  the  advanced  gastrula.  In  discussing  these  and  subsequent 
changes,  we  shall  use  the  word  "  differentiation,"  which  means 
literally  "  a  becoming  different."  Differentiation  increases 
after  the  gastrula  stage,  and  the  embryo  becomes  longer  and 
larger,  as  organ  after  organ  makes  its  appearance  out  of  one 
or  the  other  of  the  three  germ-layers.  However  small  the 
organs  may  be,  the  trained  embryologist  knows  with  a  high 
degree  of  certainty  the  origin  and  history  of  each  one  of  them. 

Before  the  gastrula  has  passed  into  a  later  stage  we  can 
observe  in  sections  cut  like  those  in  Figs.  105,  C\  1),  E,  F,  that 
the  two  large  cells  at  the  closed  end  of  the  gastrula,  called 
pole-cells,  are  giving  rise  by  division  to  a  row  of  mesodermal 
cells.  In  the  older  portion  of  the  two  rows  of  mesodermal  cells 
cavities  are  beginning  to  appear  (Fig.  106,  A,  I>).  Fig.  106,  ]> 
shows  how  a  gastrula  of  the  same  age  appears  in  cross  sec- 
tion. Ectoderm  and  endoderm  are  separated  at  the  lower 
portion  by  a  double  layer  of  mesodermal  cells,  with  a  small 
cavity  between.  The  small  cavities  are  the  beginnings  of  the 
sections  of  the  body-cavity,  found  complete  in  the  adult 
earthworm.  The  cavity  at  the  center  of  all  is  the  archenteron 
(Fig.  105,  F,  ar\  Fig.  106,  B,  ar),  which  means  old  or  primi- 
tive intestine.  The  mouth  of  the  gastrula,  which  is  called 
the  blastopore,  becomes  the  mouth  of  the  young  earthworm. 
At  the  opposite  point  a  small  opening  appears ;  this  becomes 
the  anus  of  the  young  animal.  Fig.  106,  E,  shows  how  a  lon- 
gitudinal section  through  a  young  earthworm  would  appear. 
Development  of  the  embryo  to  the  form  of  the  young  is  direct. 

As  the  body-cavity  increases  in  relative  size  the  inner 
layer  of  cells  of  the  mesoderm  becomes  applied  closely  to  the 
wall  of  the  intestine  (Fig.  106,  E,  al) ;  the  outer  layer  of  the 
mesoderm  becomes,  from  that  time  on,  a  part  of  the  outer 
wall  of  the  body-cavity  (Fig.  106,  E,  m2).  Fig.  106,  C,  D,  n 


THE  EARTHWORM 


217 


illustrates  the  development  of  the  nervous  system  out  of 
the  ectoderm.  The  organs  and  tissues  of  the  earthworm  which 
originate  from  the  germ-layers  may  be  stated  briefly  as  follows. 
From  the  ectoderm  come  the  outer  skin  and  the  nervous 
system ;  from  the  mesoderm  develop  the  muscles,  the  blood- 
vessels, the  reproductive  organs,  arid  probably  the  nephridia ; 
from  the  endoderm  comes  the  lining  of  the  alimentary  canal. 


ec 


an 


FIG.  106.   Late  Stages  of  Development  of  Earthworm.    Much  enlarged 

A,  longitudinal  section  of  gastrula,  beginning  of  portions  of  body-cavity ;  7>,  trans- 
verse section  of  gastrula,  same  stage  as  A  ;   C,  transverse  section  of  gastrula, 
body-cavity  enlarging,  mesoderm  divided ;  D,  transverse  section,  inner  por- 
tion of  mesoderm  lying  against  endoderm,  outer  portion  against  ectoderm 
E,  longitudinal  section  of  young  earthworm,  alimentary  canal  fully  formed 
ar,  archenteron  ;  an,  anus  ;  al,  alimentary  canal ;  ec,  ectoderm  ;  en,  entoderm 
coe,   body-cavity   (coelom) ;    m,    pole-cells   of   mesoderm ;    m2,    mesoderm 
mh,  mouth;  n,  ventral  nerve-chain;  s,  cavity  of  somite;  s.m,  outer  layer  of 
mesoderm ;  spl.  in,  inner  layer  of  mesoderm 

(From  Sedgwick  and  Wilson's  General  Biology} 


218  GENERAL  ZOOLOGY 

RELATION  TO  ENVIRONMENT 

We  could  find  no  better  animal  to  show  how  an  organ- 
ism may  be  adapted  to  its  environment  than  the  earthworm. 
In  the  first  place,  the  slender,  rounded  body  with  its  pointed 
anterior  end  is  the  best  possible  form  for  progression  through 
a  dense  medium,  the  substance  of  which  is  usually  displaced 
by  muscular  energy.  The  appendages,  which  in  none  of 
the  earthworm's  relatives  are  hard  enough  to  be  used  for 
digging,  are  here  reduced  to  the  minimum,  only  the  tips  of 
bristles  remaining.  The  animal  is  thus  not  impeded  by 
useless  organs.  The  smooth  skin  is  thin,  and  is  kept  moist 
for  use  as  a  breathing-surface.  Branched  gills,  such  as  are 
developed  on  many  relatives  of  the  earthworm  that  live 
in  the  sea,  would  in  the  earthworm  be  superfluous,  and 
much  in  the  way.  Reasons  that  explain  the  presence  of 
eyes  in  animals  which  live  in  the  atmosphere,  or  in  the 
water,  lead  to  the  explanation  of  the  absence  of  eyes  in 
the  earthworm. 

It  is  a  wonderful  fact  that  the  earthworm  has  no  eyes  and 
still  is  able  to  distinguish  light  from  darkness ;  for,  except  in 
the  time  of  a  rainstorm  or  in  case  of  disease,  it  never  leaves 
its  burrow  in  the  daytime.  By  means  of  the  very  simple 
sense-organs  in  the  skin  the  earthworm  can  distinguish  dif- 
ferent intensities  of  light.  It  was  found  recently  (1902), 
during  experiments  carried  on  at  Harvard  University,  that 
earthworms  not  only  appear  to  know  the  direction  from 
which  light  comes,  but  that  they  crawl  away  from  light  of 
high  intensity  and  crawl  toward  light  of  low  intensity.  Of 
course,  in  the  experiment,  they  did  this  without  reference 
to  the  matter  of  food.  In  nature,  earthworms  come  out  at 
night,  in  the  warm  seasons,  probably  in  response  to  the 
stimulus  of  a  low  intensity  of  light,  but  also  for  the  purpose 
of  obtaining  food. 


THE  EARTHWORM  219 

Earthworms  are  sensitive  to  changes  in  temperature,  al- 
though when  in  otherwise  favorable  situations  they  will 
endure  a  rise  from  18°  C.  to  28°  C.  (64.4°  F.  to  82.4°  F.)  with- 
out changing  their  position,  —  a  fact  determined  by  some 
experiments  carried  on  at  Bryn  Mawr  College.  When  earth- 
worms rest  in  the  daytime,  just  below  the  mouth  of  their 
burrows,  they  do  so  probably  as  the  result  of  at  least  four 
stimuli,  —  light,  heat,  fresh  air,  and  moisture.  If  certain  of 
these  stimuli  were  taken  away,  or  even  changed  in  degree, 
the  earthworm  would  undoubtedly  move. 

For  example,  if  the  moisture  of  the  ground  should  become 
lessened  by  continued  dry  weather,  the  animal  would  have  to 
forego  the  fresh  air  and  retreat  in  order  to  prevent  its  skin 
from  drying,  which  would  shut  off  respiration  altogether.  If 
moisture  becomes  too  great,  as  in  a  rain-storm,  the  burrows 
are  filled  with  water,  and  most  of  the  oxygen  in  the  narrow, 
close  quarters  is  driven  out  and  the  rest  is  soon  used  up. 
The  earthworm  is  then  compelled,  if  it  has  been  resting  near 
the  surface,  to  leave  its  burrow  and  crawl  about.  This  it 
may  do  in  protected  places  without  serious  results,  since  the 
heat  at  such  times  cannot  have  its  drying  effect  on  the  skin. 
When  the  storm  is  over,  those  that  are  not  caught  up  by 
birds  or  trampled  under  foot  by  large  animals  can  make  their 
way  into  the  soil  again.  When  earthworms  are  engaged  in 
boring  through  the  soil,  the  air  in  their  burrows  is  in  circula- 
tion, and  even  though  the  amount  of  oxygen  may  be  small, 
it  appears  to  be  sufficient  to  release  the  necessary  amount  of 
energy  for  their  work. 

When  animals  become  adapted  in  structure  and  habit  to 
their  environment,  the  result  is  a  definite  food-supply  and 
protection  to  themselves  and  their  race.  Certainly  the  food- 
supply  of  earthworms  is  assured  to  them,  for  besides  the  leaves 
which  they  drag  into  their  burrows,  they  are  known  to  devour 
the  soil  itself,  taking  it  into  their  mouths  as  they  burrow 


220  GENERAL  ZOOLOGY 

along.  Black  soil  called  humus  is  made  up  of  the  usual  soil- 
minerals,  mixed  with  a  large  amount  of  decaying  vegetable 
matter  and  some  animal  matter.  Completely  decayed  organic 
matter  is  that  which  has  returned  to  its  original  inorganic, 
mineral  state.  The  partially  decayed  organic  matter  can  still 
be  used  as  tissue-building  and  energy-producing  food ;  it  is 
this  which  the  earthworms  get  in  the  soil  they  swallow. 

It  is  one  of  the  habits  of  earthworms  to  come  to  the  sur- 
face at  night  to  void  the  indigestible  contents  of  the  intestine. 
The  coiled,  worm-shaped  "  castings  "  are  familiar  to  any  one 
who  has  noticed  the  ground  where  the  grass  is  thin,  even  by 
the  sides  of  much-used  pavements  in  cities.  The  soil  in  the 
castings  is  usually  brought  from  depths  varying  from  a  very 
few  inches  to  as  great  a  depth  as  five  feet.  Observations 
made  by  Darwin,  extending  over  a  period  of  more  than  forty 
years,  during  which  time  he  also  collected  facts  from  all  parts 
of  the  world  and  published  in  a  book  entitled,  The  Forma- 
tion of  Vegetable  Mould  through  the  Action  of  Worms,  are 
extremely  valuable  to  us  now,  in  showing  how  small  agencies 
acting  over  wide  areas,  through  ages  or  even  years  of  time, 
can  yield  tremendous  results. 

If  every  active  earthworm  voids  its  castings  at  the  surface, 
fallen  leaves,  sticks,  and  other  bits  of  organic  objects  will  in 
a  short  time  be  covered  with  a  thin  coating  of  earth  brought 
up  from  beneath.  The  humus  acids  present  at  all  times  in 
the  soil  attack  and  disintegrate  the  organic  matter,  thus  en- 
riching the  soil  with  the  minerals  which  the  growth  of  exten- 
sive crops  may  have  deprived  it  of.  Darwin  determined  the 
rate  at  which  objects  once  upon  the  surface  gradually  sink 
to  lower  depths.  Layers  of  cinders,  chalk,  stone,  etc.,  were 
strewn  upon  small  fields,  and  trenches  were  dug  from  year 
to  year  to  ascertain  the  progress  of  the  earthworms'  activity. 
In  fields  of  ordinary  fertility,  having  an  average  supply  of 
worms,  the  amount  of  earth  brought  to  the  surface  and  spread 


THE  EARTHWORM  221 

out  more  or  less  evenly  is  one  fifth  of  an  inch  a  year.  In  the 
course  of  comparatively  few  years  this  is  sufficient  to  conceal 
from  sight  objects  of  considerable  size.  Indeed,  Darwin  wit- 
nessed a  sterile,  stony  field  with  flints  "  as  large  as  a  child's 
head  "  transformed  into  a  fertile,  grass-covered  pasture,  "  so 
that  after  thirty  years  (1871)  a  horse  could  gallop  over  the 
compact  turf  from  one  end  of  the  field  to  the  other,  and  not 
strike  a  single  stone  with  its  shoes.  This  was  certainly  the 
work  of  worms,  for,  though  castings  were  not  frequent  for 
several  years,  yet  some  were  thrown  up  month  after  month, 
and  these  gradually  increased  in  numbers  as  the  pasture 
improved." 

Estimates  which  Darwin  based  on  careful  observations 
indicate  that  over  fifty  thousand  earthworms  find  plenty  of 
working-room  in  an  acre  of  ground,  and  that  these  bring 
to  the  surface  annually  from  fourteen  to  eighteen  tons  of 
earth. 


CHAPTER   XVII 
ALLIES  OF  THE  EARTHWORM:  VERMES 

Sinuous,  glittering  worm  of  the  sea, 
Wondrous  in  sheen  of  ruby  and  green. 

The  Sandworm.  One  of  the  commonest  of  the  animals  liv- 
ing in  the  mud  and  sand  at  tide-level  in  protected  bays  and 
inlets  of  all  the  oceans  is  the  sandworm,  known  more  defi- 
nitely by  its  scientific  name  Ne'reis  vi'rens  (Fig.  107).  It  lives 


FIG.  107.  Livin    Sandworm.    Reduced 


in  burrows  lined  with  a  thick  mucus,  which  unites  the  grains 
of  sand  into  a  tough,  black  tube.  The  depth  of  these  burrows 
depends  on  the  length  of  the  animal,  which  is  sometimes  as 
great  as  two  feet.  Like  the  earthworm,  they  often  rest  with 
the  head  near  the  opening  during  the  day;  sometimes  at  night 

222 


ALLIES  OF  THE  EARTHWORM 


223 


they  leave  their  burrows  to  swim  at  the  surface.  It  is  likely, 
however,  that  in  most  cases  they  do  not  withdraw  the  entire 
body  from  the  burrow,  but  reach  out  in  all  directions  for  prey 
that  comes  near  them.  When  driven  from  their  burrows  in 
the  daytime  they  swim  away,  and  at  that  time  look  very 
beautiful,  as  the  couplet  above  suggests.  Nereis  has  two 
horny  jaws,  sharp- 
pointed,  and  bend- 
ing to  meet  at  the 
tips.  The  jaws  are 
concealed  by  the 
infolded  pharynx 
when  not  in  use. 
When  about  to 
seize  its  prey,  which 
consists  chiefly  of 
small,  live  sea-ani- 
mals, the  sandworm 
suddenly  everts  the 
pharynx,  and  the 
jaws,  thus  freed,  at 
once  spread  hori- 
zontally and  seize 
the  victim. 

Comparison  of 
the  external  appear- 
ance of  the  sand- 
worm  with  that  of 
the  earthworm  brings  out  some  points  of  difference,  as  well 
as  some  points  of  similarity.  We  observe  the  same  division 
into  somites  of  approximately  uniform  structure  throughout 
the  body.  Fully  developed  locomotor  organs,  and  a  distinct 
head  with  eyes  and  tactile  sense-organs,  serve  to  adapt  Nereis 
to  the  necessities  of  its  environment. 


EIG.  108.  Photograph  of  Tube- Worm.    Slightly 

reduced 
1,  thread-like  gills;  2,  tentacles 


224 


GENERAL  ZOOLOGY 


The  Tube-Worm.  The  name  "  tube-worm  "  applies  equally 
well  to  many  genera  of  slender  animals  that  live  continuously 
in  tubes  of  mud,  sand,  or  limy  secretions  (Ser'pula,  in  Fig.  77) 
in  the  sea.  In  an  animal  remaining  fixed  in  the  sand,  like 
Amphitri'te  orna'ta  (Fig.  108),  it  would  seem  to  be  economy  in 
animal  architecture  not  to  have  broad  swimming  appendages 
like  those  of  its  relative,  Nereis.  On  the  same  principle  we 
observe  that  gills  (Fig.  108,  l)  occur  only  at  the  anterior  end 

where  they  may  obtain  oxygen  from 
the   circulating    water  above   the 
animal.    To  counterbalance  the  dis- 
advantage of  a  fixed  habitat,  Am- 
phitrite    has    many   long   tentacles 
(Fig.  108,  2)  which  extend  out  over 
an  area  sometimes  of  three  square 
feet.  These  tentacles  are  covered 
with  scattered  fine  bristles  and 
with   many   cilia;    the    cilia    are 
waving  constantly  toward  the  ani- 
mal's mouth,  carrying  in  the  micro- 
scopic food  present 
in    the    water.     At 
the  same  time  the 
bristles,   aided  by 
mucus  which  is  se- 
creted from  glands 
on    the    tentacles, 
catch  up  grains  of 
sand.     These    are 
added  to  the  little 
hummock  that  con- 
ceals the  mouth  of  Arnphitrite's  permanent  home. 

The  Leech.  Most  species  of  leeches  are  known  to  be  tem- 
porary parasites  on  other  animals,  but  Placobdel'la  rugo'sa 


FIG.  109.  Leech.  Slightly  reduced 


ALLIES   OF  THE  EARTHWORM  225 

(Fig.  109)  feeds  on  plants  that  grow  among  stones  and  sticks 
at  the  bottom  of  brooks.  It  is  about  two  inches  long  and 
broader  near  the  posterior  end  than  elsewhere.  The  anterior 
and  posterior  sucking-disks  on  the  ventral  surface  are  used 
for  holding  on  to  a  support,  and  for  locomotion.  Placobdella 
"loops"  itself  along,  but  it  cannot  swim,  as  some  other  species 
of  leech  can,  although  no  leeches  have  appendages. 

The  body  of  the  leech  is  divided  into  thirty-three  somites, 
and  these  are  superficially  divided  into  two  and  sometimes 
three  rings.  Two  eyes  lie  close  together  on  the  dorsal  surface 
of  the  third  somite.  The  mouth  is  on  the  ventral  surface  near 
the  anterior  sucking-disk.  The  pharynx  can  be  rolled  out  as 
in  Nereis.  The  color  of  Placobdella  is  described  by  Professor 
Moore,  of  the  University  of  Pennsylvania,  as  a  "  pepper-and- 
salt  mixture  of  various  light  and  dark  browns,  yellows,  and 
greens."  Around  the  margin  are  light-colored  patches. 

Leeches  are  hermaphroditic.  Placobdella  rugosa  carries  its 
eggs  in  a  gelatinous  mass  on  the  ventral  surface.  When  the 
young  hatch  they  live  for  several  weeks  attached  by  the  pos- 
terior sucker  to  the  parent,  as  shown  in  the  picture. 

Definition  of  Annulata  (Lat.  ^anmdus,  a  ring).  The  earth^ 
worm,  sandworm,  tube-worm,  and  leech  have  certain  charac- 
ters in  common.  The  body  is  divided  into  somites  of  nearly 
uniform  shape,  the  characteristic  form  being  a  ring.  From  that 
resemblance  the  name  of  the  phylum  Annula'ta,  also  called 
Anneli'da,  is  derived. 

Two  classes  are  represented  by  these  four  animals:  the 
Chcetop'oda  (bristle-footed),  by  Lumbricus,  Nereis,  and  Am- 
phitrite  ;  and  the  Hirudin'ea  (Lat.  hirudo,  leech),  by  Placob- 
della. 

The  Flatworm.  On  the  lower  surface  of  submerged  stones, 
near  the  margin  of  ponds,  there  are  many  little  black,  or  white, 
flatworms.  The  most  of  these  belong  to  a  genus  called  Pla- 
na'ria.  Quite  often  a  larger  specimen  (10  mm.  to  15  mm.)  is 


226 


GENERAL  ZOOLOGY 


FIG.  110.  Flat- 
worm,     x  10 


found  among  the  others.  This  is  most  likely  to  belong  to  the 
species  Dendrocoe'lum  lac'teum  (Fig.  110).  It  is  nearly  color- 
less except  for  a  clouded  middle  region.  Upon 
examination  with  a  simple  lens  an  observer  may 
distinguish  the  organs  of  the  interior  with 
remarkable  clearness.  The  mouth  is  in  the 
middle  of  the  under  surface.  It  is  at  the  end 
of  a  short  proboscis  (the  pharynx)  which  may 
be  rolled  inside  out.  Microscopic  food  entering 
the  mouth  may  pass  forward  through  a  slender 
tube,  and  into  all  of  the  many  branches,  or  it 
may  pass  backward  by  two  tubes  and  into  their 
branches.  Since  every  part  of  the  body  has  its 
branch  from  the  digestive  tubes,  the  animal 
does  not  need  a  blood-system.  At  the  anterior 
end  beneath,  there  is  a  shallow  sucker  for  hold- 
ing on  to  stones  or  plants.  Above  there  is  a 
pair  of  small  eyes  of  very  simple  structure.  The  body  is  not 
divided  into  somites.  Each  individual  is  hermaphroditic. 

The  class  to  which  Dendrocoelum  lacteum  belongs  is  called 
Turbella'ria  (Lat.  turbo,  a  whirling,  referring  to  the  move- 
ment of  water  about  the  mouth). 

The  Trematode.  Animals  of  the  appearance  of  Dis'tomum 
somater'ice  (Fig.  Ill)  are  not  often  seen,  because  they  are 
parasitic  in  the  bodies  of  other  animals.  This  species  infests 
the  bodies  of  mussels,  and  as  already  stated,  is  now  believed  to 
be  the  indirect  cause  of  pearls  being  found  in  those  animals 
(see  p.  174).  The  figure  represents  the  parasite  in  a  stage 
which  is  nearly  adult. 

The  ventral  surface  of  the  body  has  two  sucking-disks,  one 
at  the  anterior  end  (Fig.  Ill,  1)  and  one  near  the  middle  (Fig. 
Ill,  5).  They  are  for  holding  on.  The  mouth  is  at  the  cen- 
ter of  the  anterior  disk,  and  is  connected  by  a  short  tube  with 
a  wide  pharynx  (Fig.  Ill,  2).  The  gullet  is  divided  into  a 


ALLIES  OF  THE  EARTHWORM 


227 


right  and  left  branch  which  open  into  sacs  (Fig.  Ill,  3).  Food 
taken  into  these  sacs  passes  by  osmosis  into  the  tissues.  The 
granular  masses  (Fig.  Ill,  4)  are  the  excretory  organs.  In  this 
stage  the  ovaries  and  spermaries  are  not  developed ;  these 
organs  occur  together  in  each  adult.  The  body  is  not  divided 
into  somites. 

The  life-history  of  these  parasites  is  usually  very  com- 
plicated. Professor  H.  L.  Jameson  believes  that  Distomum 
somaterise  begins  its  life  in  a  clam 
found  on  the  coast  of  France.  At  a 
certain  stage  the  young  leave  the 
clam  and  make  their  way  into  the 
mussel,  Mytilus  edulis  (see  Fig.  126). 
The  mussels  are  eaten  by  the  black 
scoter,  a  sea-duck,  and  in  the  body 
of  the  bird  the  eggs  of  the  parasite 
are  produced  and  sent  out.  By  some 
chance  the  larvse  enter  the  clam, 
and  thus  complete  the  cycle  of  devel- 
opment. 

The  class  to  which  this  parasite  be- 
longs is  called  Tremato'da  (Gr.  trema, 
hole  ;  eidos,  form,  referring  to  appear- 
ance of  suckers). 

The  Tapeworm.  The  best-known 
tapeworm  is  the  one  that  is  sometimes 
found  to  inhabit  the  intestine  of  man, 
Tce'nia  sagina'ta  (Fig.  112).  This  parasite  frequently  grows  to 
the  length  of  many  feet.  The  figure  seems  to  show  that  the 
body  is  divided  into  somites,  but  these  divisions  are  not  con- 
sidered true  somites.  The  head  of  the  animal  is,  except  for 
the  narrow  neck  behind  it,  the  smallest  portion  of  the  body ; 
the  posterior  portion  is  the  oldest  part  of  the  parasite,  except 
the  head  itself.  New  somite-like  divisions  of  the  body  form 


FIG.  111.  Treinatode. 
Much  enlarged.  (After 
Jameson) 

1,  anterior  sucking-disk, 
and  mouth ;  2,  pharynx ; 
3,  digestive  sac;  4,  excre- 
tory organs ;  5,  posterior 
sucking-disk 


228 


GENERAL   ZOOLOGY 


just  behind  the  head,  and  as  they  grow  older  and  larger  are 
pushed  backward  by  newer  ones.  The  tapeworm  is  an  inter- 
esting example  of  a  parasite  that  has  become  so  completely 
dependent  on  its  host  that  one  of  the  most  important  systems 
of  the  body  has  totally  disappeared,  namely  the  digestive 
system.  The  parasite  maintains  its  hold  on  the  inner  wall  of 
the  intestine  by  four  sucking-disks  on  the  head  ;  the  body  floats 
free  in  the  intestine,  and  food  can  be  absorbed  from  all  sides. 
Every  tapeworm  has  in  each  division  both 
eggs  and  spermatozoa.  The  spermatozoa  ferti- 
lize the  eggs  in  the  same  division.  When  the 
embryos  reach  a  certain  stage,  a  few  terminal 
divisions  of  the  adult  separate  from  the 
rest,  and  pass  out  with  the  undigested 
portion  of  the  person's  food.  Sometimes 
the  embryos,  inclosed  in  their  thick  mem- 
branes, are  swallowed  by  cattle  while 
drinking  at  pools.  In  the  intestine  the 
membrane  of  the  embryo  is  dis- 
solved, and  the  freed  larva  bores 
its  way  through  the  wall  of  the 
intestine,  and  finally  comes  to 
rest  in  the  muscular  tissue.  It 
remains  there  until  the  muscle 
is  consumed  in  a  partially  raw 
state  by  man ;  then  in  his  intestine 
the  young  animal  develops  into 
the  adult,  mature  tapeworm.  An- 
other species  of  tapeworm  (Tcvnia 
so'lium),  found  in  human  beings, 
comes  from  uncooked  pork. 


FIG.  112.  Tapeworm.  Left-hand 
drawing,  reduced ;  right-hand 
drawing,  enlarged.  (After 
Leuckart) 


Tapeworms  are  not  necessarily  fatal.  The  annoyance  is  con- 
siderable, however,  until,  by  a  period  of  fasting  jgid  medical 
treatment,  the  life  of  the  head  of  the  parasite  is  destroyed. 


ALLIES   OF  THE   EARTHWORM 


229 


The  class  to  which  the  tapeworms  belong  is  called  Ccsto'da 
(Gr.  kestos,  girdle;  eidos,  form). 

Definition  of  Platyhelminthes  (Gr.  platys,  flat ;  helmins, 
worm).  The  three  classes,  Turbellaria,  Trematoda,  and  Ces- 
toda,  constitute  the  phylum  Platyhel- 
min'thes.  The  members  of  this  phylum 
are  worms  with  flattened  bodies,  that 
are  not  divided  into  somites.  All  the 
species  are  hermaphroditic. 

Trichina.  Trichi'na  spira'lis  (Fig. 
113,  1)  is  one  of  the  most  dangerous 
of  parasites.  Like  the  tapeworm  it 
requires  two  hosts  to  complete  its  de- 
velopment. The  adult  Trichina  may 
be  found  in  the  intestine  of  a  pig,  rat, 
or  of  man.  The  female  Trichina,  about 
3  mm.  (|  in.)  long,  brings  forth  its  young 
alive ;  the  young  ones  bore  their  way 
through  the  intestine  and  along  the  thin 

connective  tissue  of  the  trunk  or  legs. 

rr(1  ,,  ,     .  FIG.  113.  Trichina.  Much 

Ihere  they  come  to   rest,  and   inclose        enlarged.    (After 

themselves  in  a  thick,  tough  membrane 
or  cyst  (Fig.  113,  2),  remaining  encysted 
until  the  muscle  is  eaten  by  another 
animal.  Then  the  cyst  dissolves,  per- 
mitting the  young  and  still  undeveloped  Trichina  to  grow  and 
reach  maturity  in  the  intestine  of  the  second  host.  If  the 
first  host  is  the  pig,  the  second  host  may  be  the  human  being. 
The  danger  to  the  human  being  comes  while  the  young 
are  making  their  way  into  the  muscular  tissue.  The  boring 
of  thousands  and  sometimes  millions  of  these  larval  parasites 
in  the  muscles  disintegrates  the  tissue  and  causes  a  fever, 
which  is  very  frequently  fatal.  A  simple  preventive  remedy, 
which  every  one  should  apply,  is  to  see  that  all  pork  eaten 


Leuckart) 

1,  parasite;  2,  membrane 
of  cyst;  3,  muscle-fiber 
of  pig 


230 


GENERAL  ZOOLOGY 


is  well  cooked.  The  Bureau  of  Animal  Industry,  United 
States  Department  of  Agriculture,  has  officials  at  all  the 
large  packing  institutions,  who  examine  microscopically  for 
Trichina  and  tapeworm  larvse  some  of  the  muscle  of  every 
animal  killed. 

Trichina  belongs  to  the  class  Nemato'da  (Gr.  nema,  thread ; 
eidoB,  form)  and  the  phylum  Nemathelmin'thes  (Gr.  nema, 
thread ;  helmins,  worm). 

The  Rotifer.  Sometimes  when  we  examine  with  the  com- 
pound microscope  the  contents  of  a  small  drop  of  stagnant 
water,  we  find  very  small,  conical- 
shaped  animals  (Fig.  114),  with  two 
spines  at  the  end  of  a  short  tail, 
"looping"  across  the  field  of  vision 
with  considerable  vigor.  Occasionally 
they  cease  the  inch-worm  method  of 
getting  along,  and  whirl  away  by 
means  of  one  or  two  circular  rows  of 
cilia  (Fig.  114,  l)  at  the  broad,  ante- 
rior end.  These  animals  are  called 
rotifers.  A  common  species  is  Brachi- 
o'nus  urceola'ris.  In  length  they  are 
about  .3  mm.  (^  in.).  Although  very 
small,  they  possess  a  complete  diges- 
tive system,  with  mouth,  pharynx, 
grinding-apparatus,  stomach,  diges- 
tive gland,  intestine  and  anus,  an 
excretory  system  (no  circulatory 
system),  nervous  .system,  sense-organs, 
and  reproductive  system.  The  indi- 
viduals are  male  or  female,  but  the 
male  is  to  be  found  only  in  the  fall  of  the  year,  and  even 
then  rarely.  It  is  about  one  fourth  as  large  as  the  female. 
In  some  species  of  rotifers  the  male  is  unknown. 


FIG.  114.  Rotifer.     Much 
enlarged.   (After  Weber) 

1,  cilia ;  2,  nerve-ganglion  ; 
3,  eggs  forming  ;  4,  eggs 
formed;  5,  excretory 
organs,  n  e  p  h  r  i  d  i  a  ; 
6,  terminal  spines 


ALLIES  OF  THE  EARTHWORM  231 

There  may  be  more  than  one  generation  of  females  produced 
in  the  spring  and  summer  from  large  eggs,  which  undergo 
development  while  attached  near  the  tail  of  the  parent  (Fig. 
114,  4).  These  eggs  develop  parthenogenetically  (see  p.  34). 
The  large  eggs  always  produce  females.  Under  certain  con- 
ditions some  small  eggs  are  formed.  These  develop  with- 
out fertilization  into  males.  In  the  autumn  the  females  form 
"  winter  eggs,"  which  are  fertilized  by  spermatozoa  from  the 
males.  The  fertilized  eggs  lie  dormant  through  the  winter 
and  develop  into  females  in  the  spring. 

Members  of  the  class  to  which  Brachionus  belongs  (class 
Motif  era)  are  found  in  bodies  of  water,  both  salt  and  fresh, 
all  over  the  world.  Certain  species  live  in  swamps,  others  at 
the  bottom  of  deep  water,  others  still  at  the  surface.  No 
matter  how  great  the  distance,  the  same  species  appears  to 
be  present  in  situations  that  have  approximately  identical 
conditions.  This  is  accounted  for  partly  by  the  fact  that  the 
eggs  will  endure  drying  in  the  mud,  and  in  that  condition 
may  be  scattered  over  wide  areas  by  being  carried  on  the 
feet  of  birds,  or  by  being  blown  about  by  the  wind.  Thus 
they  have  the  opportunity  of  developing  in  places  exactly 
suited  to  them.  The  phylum  is  called  Trochelmin'thes  (Gr. 
troches,  wheel;  helmins^  worm). 

Plumatella.  There  are  many  animals  which,  in  their  habit 
of  living  attached  to  some  object  throughout  life,  resemble 
plants.  Some  of  them  live  in  a  mass  composed  of  many 
individuals,  so  closely  connected  with  one  another  that  we 
give  the  name  "colony "to  the  entire  collection.  In  the  case 
of  Plumatel'la  re' pens  (Fig.  115)  the  individual  zooids  (mem- 
bers of  the  compound  organism)  are  connected  by  a  system 
of  branching,  but  the  vital  organs  of  each  are  not  connected 
with  those  of  any  other  zooid.  A  colony  of  Plumatella  grows 
in  a  small,  roughly  branched  mass  around  a  dead  submerged 
twig  in  fresh-water  ponds. 


232 


GENERAL  ZOOLOGY 


Each  zooid  is  microscopic  in  size,  but,  as  in  the  rotifers, 
we  can  identify  definite  and  rather  highly  organized  internal 

organs.  The  mouth 
is  surrounded  by  a 
circle  of  tentacles 
that  have  the  func- 
tion of  creating  cur- 
rents in  the  water, 
on  which  food  and 
oxygen  are  carried 
to  the  animal.  The 
circle  of  tentacles 
is  called  the  lopho- 
phore  (Fig.  115,  1). 
From  the  mouth 
the  food  passes 
by  a  short  gullet 
(Fig.  115,  3)  to  the 
stomach.  The  in- 
testine is  bent  on 
the  stomach  in 
such  a  way  that  it 
opens  on  the  ex- 
terior (Fig.  115,  4), 
just  outside  the 
circle  of  tentacles, 
giving  the  whole 
FIG.  115.  Plumatella.  Upper  portion  of  figure  alimentary  canal 
much  enlarged;  lower  portion,  slightly  enlarged,  something"  of  the 
(After  Allman) 

appearance   of  the 

letter  I).    Other 
organs  are  a  gan- 
glion between  the  mouth  and  the  anus,  a  pair  of  nephridia  for 
excretion,  an  ovary  and  a  spermary,  muscles  which  withdraw 


1,  lophophore  ;  2,  chitinous  sheath;  3,  gullet;  4,  anus; 
5,  statoblast 


ALLIES  OF  THE  EARTHWORM 


233 


the  body  into  the  chitinous  sheath  (Fig.  115,  2),  and  other 
muscles  to  extend  the  body  again.  Plumatella  reproduces 
by  eggs  and  spermatozoa,  by  budding,  and  by  statoblasts 
(Fig.  115,  5).  Statoblasts  are  internal  buds  developed  from 
cells  lying  upon  the  retractor  muscle,  and  are  covered  with  a 
chitinous  shell.  In  case  the  colony  freezes  in  winter,  or  the 
pond  dries  up,  the  statoblasts  remain  alive,  and  on  the  return 
of  favorable  conditions  start  a  new  generation. 

The  class  of  which  Plumatella  is  an  example  is  called 
sometimes  Polyzo'a,  and  sometimes  Bryozo'a.  Most  of  the 
members  of  the  class  live  in  the  sea  as  mat-like  or  moss-like 
fixed  colonies.  On  account  of  their  brownish  color  and  deli- 
cate texture  some  of  these  colonies  are  fre- 
quently mistaken  for  brown  seaweeds. 

The  Brachiopod.  The  first  impression  that 
the  casual  observer  has  of  the  animal  repre- 
sented in  Fig.  116  (Lin'gula  lepid'ula)  is  that 
he  is  looking  at  some  kind  of  a  clam,  — 
an  impression  given  by  the  two  calcareous 
valves  which  inclose  the  body  proper ;  but 
the  brachiopod  is  not  a  clam.  It  lives  at  the 
bottom  of  bays,  and  is  found  most  abundantly 
in  the  waters  of  Japan.  It  has  a  shell  from 
one  half  inch  to  one  inch  in  length,  and  a 
stalk  called  the  peduncle,  two  or  three  times  FIG.  116.  Brachi- 
as  long.  Professor  E.  S.  Morse,  of  Salem,  °P°d-  Natural 
Massachusetts,  has  witnessed  the  activities 
of  various  species  of  these  animals,  and  has 
written  interestingly  6f  their  habits.  When  undisturbed  in 
a  sea-water  aquarium,  Crlottid'ia  pyramida'ta  (Fig.  117)  lies 
with  part  of  its  body  above  the  sand.  The  valves  open 
slightly,  and  the  bristles,  extending  from  between  the  valves, 
are  grouped  roughly  into  three  tubes.  The  lophophore  makes 
a  waving  motion  which  sets  up  currents  in  the  water,  as 


size.   (After 
Morse) 


234  GENERAL  ZOOLOGY 

shown  by  the  arrows.  Through  two  of  these  improvised  tubes 
solid  (microscopic)  food  is  carried  in  ;  through  the  middle  one 
the  unused  particles  and  the  excreted  wastes  of  the  body  are 
sent  away.  The  bristles  are  useful  in  affording  a  surface 
for  microscopic  organisms  to  grow,  which  later  become  food 

for  their  larger  table-mate ;  the 
bristles  are  also  useful  in  pre- 
venting sand  from  entering  the 
cavity  between  the  valves. 

The  internal  organs  are  very 
much  the  same  as  in  Pluma- 
tella.  In  fact, 
the  nearest  liv- 
ing relatives  of 
Lingula  and  its 

close  allies,  the 
FIG.  117.   Brachiopod.    Enlarged.   (After  Morse) 

members  of  the 

class  Brachiop'oda,  are  thought  to  be  the  class  Polyzoa. 
Brachiopods  are  among  the  oldest  of  animal  groups.  The 
valves  of  ancient  brachiopods  found  in  strata  of  rock  indi- 
cate that  the  class,  many  millions  of  years  ago,  was  far  more 
abundant  than  it  is  now,  and  also  that  the  structure  of  the 
animals  has  changed  little  in  all  that  time. 

O 

The  phylum  represented  by  Plumatella  and  Lingula  is 
known  by  the  name  Molluscoi' da,  because  of  their  formerly 
supposed  relationship  to  the  Mollusca. 

Definition  of  Vermes  (Lat.  vermis,  a  worm).  The  task  of 
summing  up  the  characteristics  of  the  Arthropoda  was  a 
comparatively  simple  one,  but  the  "  worms"  comprise  such 
a  varied  lot  of  widely  different  forms,  that  no  important  set 
of  structural  characteristics  can  be  found  that  tends  to  unite 
them  into  a  clearly  defined  group.  The  old  systems  of  classi- 
fication employed  the  term  "  Ver'mes  "  as  the  name  of  a  sub- 
kingdom,  to  include  all  those  animals  that  had  a  long,  slender, 


ALLIES  OF  THE  EARTHWORM  235 

worm-like  form.  Many  animals  that  have  such  a  form  have 
been  taken  out  of  that  branch  of  the  system  and  placed  in 
another  group,  because  their  discovered  relationship  required 
it.  On  the  other  hand,  animals  like  the  brachiopods  and  the 
polyzoans  were  once  classed  with  clams,  mussels,  and  snails, 
because  all  possessed  a  shell ;  they  are  now  thought  to  be 
more  nearly  related  to  animals  like  the  earthworm  and  other 
annelids  than  they  are  to  the  clams. 

So  true  is  it  that  no  single  characteristic  of  structure  can 
be  found  that  tends  to  unite  the  organisms  classed  as  worms 
into  a  well-defined  group,  that  systematists  are  accustomed 
to  say  that  Vermes  include  all  animals  that  are  not  clearly 
members  of  some  other  large  group.  This  does  not  indicate 
any  imperfection  in  the  bodily  structure  of  the  members  of 
the  group ;  it  means  that  our  knowledge  of  animal  morphol- 
ogy is  broken  and  incomplete,  partly  from  lack  of  complete 
investigation,  but  chiefly  because  some  organisms  that  must 
have  filled  up  the  "gaps"  in  the  chain  of  relationships  have 
disappeared  entirely,  leaving  no  trace  even  in  fossils.  The 
little  basis  we  have  for  grouping  all  the  forms  discussed  in 
Chapters  XVI  and  XVII  into  the  group  Vermes  is  found  in 
the  tendency  of  the  body  to  show  a  greater  or  a  less  degree 
of  metamerism  (division  into  somites),  either  in  the  adult  or 
in  the  embryo.  In  these  somites  the  characteristic  excretory 
organ,  the  nephridium,  most  highly  developed  in  Nereis  and 
Lumbricus,  is  nearly  always  present.  In  some  of  the  mem- 
bers of  the  group  several  pairs  of  nephridia  occur  with  no 
other  evidence  of  metamerism.  Whenever  appendages  occur 
among  Vermes  they  are  never  jointed,  as  they  are  in  Arthrop- 
oda.  Perhaps  the  strongest  indication  of  relationship  exist- 
ing between  widely  differing  members  of  the  groups,  as,  for 
example,  Annulata  and  Molluscoida,  is  to  be  found  in  the 
great  similarity  of  a  certain  stage  of  the  free-swimming  larvse 
of  the  two  phyla. 


CHAPTER   XVIII 
THE  STARFISH  AND  SOME  ALLIES:    ECHINODERMA 

Let  the  mere  star-fish  in  his  vault 

Crawl  in  a  wash  of  weed,  indeed, 
Rose-jacynth  to  the  finger-tips. 

ROBERT  BROWNING. 

THE  STARFISH 

Habitat  and  Distribution.  The  purple  starfish  (Aste'rias 
vulya'ris,  Fig.  118)  is  found  most  abundantly  north  of  Cape 
Cod  in  tide-pools  on  rocky  shores,  and  in  deep  water  near 
the  shore.  It  is  only  in  the  warmer  season,  however,  that  one 
may  witness  a  scene  like  that  portrayed  in  the  illustration. 
When  the  winter  storms  come  on,  starfishes  and  'many  other 
tide-pool  animals  that  are  not  fixed  permanently  migrate  to 
the  deeper  water,  in  order  to  be  in  more  protected  places. 

External  Structure.  Up  to  this  chapter  we  have  been  giv- 
ing our  attention  to  animals  that  have  a  perfect,  or  slightly 
modified,  bilateral  symmetry.  The  starfish  evidently  has  a 
plan  of  structure  for  which  we  must  find  some  other  name. 
In  a  specimen  we  observe  five  arms  extending  from  a  central 
region.  The  position  of  the  arms  with  reference  to  the  cen- 
tral region  or  disk  is  practically  the  same  as  the  position  of 
radii  in  a  circle.  Hence  we  say  that  the  starfish  is  radially 
symmetrical.  We  find  it  necessary  also  to  change  a  few 
terms  of  location.  In  the  picture  of  the  tide-pool  study  we 
are  looking  down  upon  the  aboral  surface  of  the  three  star- 
fishes. The  opposite  side  has  the  mouth  at  the  center,  and 
for  that  reason  is  called  the  oral  surface. 

The  aboral  surface  and  part  of  the  oral  surface  of  Asterias 
is  thickly  set  with  calcareous  spines  that  arise  from  small 

236 


FIG.  118.   Tide-Pool  Study  of  Starfishes,  East  Point,  Nahant,  Mass. 


237 


238 


GENERAL  ZOOLOGY 


plates  of  the  same  material  just  within  the  skin.  The  spines 
of  the  oral  surface  are  longer  and  more  pointed  than  those  of 
the  aboral  surface.  By  examining  the  aboral  spines  with  a 
hand-lens  one  can  make  out  a  circle  of  very  minute  struc- 
tures surrounding  the  base.  Each  of  these  structures  consists 


12 


10 


FIG.  119.  Dissection  of 
the  Starfish  (Asterias 
vulgaris).  Aboral  view. 
Slightly  reduced 


stomach-pouch ;  2,  tube  of 
pyloric  caeca;  3,  pyloric 
caecum;  4,  pyloric  csecum, 

cross  section  ;  5,  intestinal 
creca:  0,anus;  7,  retractor 
muscle  of  stomach ;  8,-sieve- 
plate ;  9,  ampulla ;  10,  tube- 
foot;  11,  ambulacral 
plates;  12,  reproductive 
gland;  13,  reproductive 
gland,  cross  section; 
14,  position  of  eye ;  15,  re- 
generating ray 


of  a  short  stalk  supporting  two  branches  that  open  and  close 
like  nippers.  These  short  stalks  with  their  branches  are 
called  pedicellarioe.  Their  use  is  unknown,  but  they  may 
rid  the  aboral  surface  of  undesirable  matter. 

Along  the  middle  of  the  oral  surface  of  each  arm  there  is  a 
groove  which  begins  at  the  mouth  and  ends  near  the  tip.  The 
roof  of  the  groove  is  formed  by  two  series  of  flat,  calcareous 


THE  STARFISH  AND   SOME  ALLIES 


239 


plates  setting  together  like  the  rafters  of  a  frame  house. 
Between  the  plates  four  rows  of  slender,  flexible  tube-feet 
(Fig.  120,  ab)  extend  to  the  outside.  The  groove  is  called 
the  ambulacral  groove,  because  it  protects  the  ambulacral 
organs  (Lat.  ambulare,  to  walk).  A  few  of  the  ambulacral 
organs  (tube-feet)  near  the  tips  of  the  arms  are  sense-organs 
for  "smelling"  food.  The  remainder  are  the  organs  of  loco- 
motion. At  the  very  end  of  each  arm  there  is  a  small  red 
eye  protected  by  a  circle  of  spines. 

The  Water-Vascular  System.  On  the  aboral  surface  at  one 
of  the  angles  between  the  arms  lies  a  lens-shaped  structure 
(Fig.  11 9,  8;  Fig.l20,w;  Fig. 
121,  10).  This  is  the  sieve- 
plate,  sometimes  known  by 
the  name  madreporic  body. 
The  plate  is  perforated  with 
fine  holes  through  which  sea- 
water  passes  to  the  stone-canal 
(Fig.  120,  s  ;  Fig.  121,  11). 
Near  the  mouth  the  stone- 
canal  joins  the  ring-canal 
(Fig.  120,  r;  Fig.  121,  12), 
which  in  turn  joins  five 
radial  canals  (Fig.  120,  c\  Fig. 
121,  13)  that  extend  through 
the  middle  of  the  roof  of  the 
ambulacral  groove.  Many 
short  tubes  branch  off  in  pairs 
from  the  radial  canals  and 
join  the  tube-feet.  At  the 
exposed  end  of  a  tube-foot  is 
a  sucking-disk  ;  at  the  inner  end  is  a  bulb-shaped  expansion, 
the  ampulla  (Fig.  119,  9  ;  Fig.  120,  a ;  Fig.  121, 14).  From  the 
sieve-plate  to  the  tube-feet  there  is  a  continuous  cavity,  and 


FIG.  120.   Ambulacral  System  of 
Starfish 

a,  ampullae;  ab,  tube-feet;  c,  radial 
canal ;  m,  sieve-plate ;  ?^,  radial  nerve ; 
p,  Poliau  vesicle ;  r,  ring-canal,  with 
nerve-ring  beneath ;  ,s,  stone-canal ; 
t,  Tiedemann's  vesicle 

(From  Hertwig-Kingsley's  Manual  of 
Zoology) 


240  GENEPxAL   ZOOLOGY 

because  of  the  fact  that  water  passes  through  the  entire  set 
of  tubes  it  is  called  the  water-vascular  system. 

This  set  of  organs  is  a  mechanism  which  enables  the  star- 
fish to  move.  The  stone-canal  being  inclosed  in  a  sheath  of 
calcareous  substance  has  a  constant  diameter,  and  so  have  the 
ring-canal  and  the  radial  canals ;  but  the  ampullse  and  the 
tube-feet  are  not  inclosed  by  an  unyielding  cover,  and  hence 
they  can  increase  and  decrease  the  volume  of  their  contin- 
uous cavity.  Preparation  for  locomotion  is  made  when  the 
ampulla  by  contracting  causes  the  water  to  close  a  valve  at 
the  branch  from  the  radial  canal,  and  then  forces  the  contained 
.vater  into  the  cavity  of  the  tube-foot.  Simultaneously  with 
the  act  of  forcing  water  into  the  tube-feet,  circular  muscle- 
libers  in  those  organs  contract  and  cause  the  water  to  extend 
them  to  their  greatest  length.  Next,  the  sucking-disks  fasten 
to  some  object,  it  may  be  even  a  smooth  surface  like  the  glass 
side  of  an  aquarium  tank.  The  longitudinal  muscle-fibers 
in  the  tube-feet  then  contract  and  drive  the  contained  water 
back  to  the  ampullae.  When  the  hundreds  of  tube-feet  in  the 
advancing  arms  of  a  starfish  are  contracting  to  pull  the  body 
along  and  extending  to  renew  their  hold,  the  arms  themselves, 
turned  up  a  little  on  the  tips,  remain  in  a  more  or  less  set 
attitude,  although  they  may  bend  now  and  then  to  pass  an  ob- 
struction. When  it  is  necessary  the  animal  can  bend  its  arms 
and  central  disk,  and  pass  through  seemingly  impossible  holes. 

The  Digestive  System.  The  mouth  (Fig.  121,  1)  is  a  circular 
opening  surrounded  by  a  thin,  circular  membrane,  the  lip. 
There  is  ho  oesophagus,  for  the  stomach  (Fig.  121,  2)  begins 
at  the  mouth  and  occupies  the  greater  portion  of  the  central 
disk,  besides  extending  two  short  pouches  (Fig.  119,  l ;  Fig. 
121,  3)  into  every  arm.  At  the  aboral  end  of  the  stomach  five 
tubes  branch  off  (Fig.  119,  2;  Fig.  121,  5)  and  are  divided 
again  into  ten  pyloric  cceca  (Fig.  119,  3;  Fig.  121,  6).  The 
cavities  of  these  organs  are  continuous  with  the  cavity  of  the 


THE  STARFISH  AND   SOME  ALLIES  241 

stomach.  The  function  of  the  pyloric  caeca  is  digestive ; 
they  secrete  a  fluid  analogous  to  the  digestive  fluid  of  the 
earthworm  and  the  clam.  The  short  intestine  sends  off  two 
branches,  which  again  divide.  These  branches  are  called  the 
intestinal  cceca  (Fig.  119,  5;  Fig.  121,  7).  Their  function  is 
to  increase  the  absorbing  surface  of  the  intestine.  The  intes- 
tine ends  at  the  anus  (Fig.  119,  6;  Fig.  121,  8),  which  lies 
near  the  center  of  the  aboral  surface. 

Asterias  feeds  on  oysters,  mussels,  clams,  and  snails.    Many 
fanciful  theories  have  been  proposed  in  the  effort  to  explain 


16    /    12   2  //    9  3     14   IS  13 


FIG.  121.    Dissection  of  the  Starfish  (Asterias  vulgaris),  oral-aboral  section. 
Slightly  reduced 

1,  mouth;  2,  stomach;  3,  stomach-pouch ;  4,  interradial  pouch  of  intestine ;  5,  cav- 
ity of  pyloric  caecum  ;  6,  pyloric  caecum  ;  7,  intestinal  caecum  ;  8,  anus ;  9,  re- 
tractor muscle  of  stomach;  10,  sieve-plate;  11,  stone-canal;  12,  ring-canal; 
13,  radial  canal ;  14,  ampulla^  15,  tube-foot ;  16,  nerve-ring ;  17,  radial  nerve ; 
18,  reproductive  gland ;  19,  calcareous  plate 

how  the  starfish  is  able  to  get  at  the  soft  parts  of  animals 
with  thick,  heavy  shells.  The  method  employed  is  totally  dif- 
ferent from  that  which  any  one  seems  to  have  imagined  before 
Professor  Schiemenz,  of  Germany,  discovered  it  in  1896.  His 
published  results  were  corroborated  by  Professor  Mead,  of 
Brown  University,  in  1899.  By  referring  to  Fig.  118,  at  the 
lower  end  of  the  illustration,  we  can  see  the  attitude  of 
Asterias  when  it  has  captured  a  sea-mussel.  While  crawling 
along  the  bottom  the  hungry  starfish  "  smells  "  its  prey  by 
means  of  the  tube-feet  at  the  tip  of  the  arms.  It  then  moves 


242  GENERAL  ZOOLOGY 

in  the  direction  of  the  mussel  and  arches  itself  over  the  shell, 
touching  the  bottom  all  around  with  the  tips  of  its  arms. 
Next  it  turns  the  mussel  about,  until  the  hinge-ligament  rests 
on  the  bottom  and  the  free  edges  of  the  closed  valves  lie  just 
beneath  the  captor's  mouth.  Then  the  starfish  takes  a  firm 
hold  on  the  bottom  with  the  tube-feet  of  the  outer  portion 
of  its  arms,  and  simultaneously  applies  the  suckers  of  the 
remaining  tube-feet  to  both  valves  of  the  mussel. 

Then  the  struggle  begins.  The  mussel  has  long  before  closed 
its  valves  tightly  by  means  of  its  tAvo  strong  adductor  muscles, 
and  the  only  way  the  starfish  can  get  at  the  soft  parts  is  to 
force  the  valves  open.  This  it  does  by  a  long-continued,  steady 
pull  on  the  surface  of  the  valves,  with  two  sets  of  tube-feet 
drawing  in  opposite  directions.  The  mussel  has  great  momen- 
tary strength,  but  it  seems  to  be  as  difficult  for  it  to  keep 
up  the  strain  as  it  is  for  a  man  to  hold  out  his  arm  several 
minutes  at  a  time.  A  single  tube-foot  of  the  starfish  is  very 
weak,  and  the  combined  strength  of  all  its  tube-feet  measures 
less  than  the  momentary  strength  of  a  mussel.  But  the  star- 
fish can  exert  much  less  than  its  full  strength,  and  open  the 
valves  of  a  mussel  within  from  fifteen  to  thirty  minutes. 

As  soon  as  the  valves  of  the  mussel  are  open  a  few  milli- 
meters the  starfish  contracts  certain  muscles  in  its  body-cavity, 
which  bring  the  stomach  down  toward  the  oral  surface  and 
cause  it  to  pass  through  the  mouth-opening,  turning  inside 
out  on  its  way.  The  everted  stomach  is  applied  to  the  soft 
body  of  the  mussel,  and  digestion  and  absorption  begin  im- 
mediately. With  slight  variations  this  is  the  method  which 
starfishes  employ  in  opening  and  digesting  oysters,  snails,  and 
other  mollusks. 

The  Circulatory,  Respiratory,  and  Excretory  Systems.  The 
circulatory  system  is  too  small  to  be  indicated  in  drawings 
on  the  scale  of  the  dissection  drawings.  A  circular  blood-vessel 
4ies  just  below  the  ring-canal  of  the  water-vascular  system, 


THE  STARFISH  AND   SOME  ALLIES  243 

and  sends  a  branch  into  each  arm  below  the  radial  canal.  The 
body-cavity  is  filled  with  a  fluid  similar  to  the  blood,  which 
is  colorless.  The  system  of  blood-vessels  is  not  complete. 

The  body  gets  much  of  the  oxygen  it  needs  by  way  of  the 
water-vascular  system.  The  remainder  conies  in  through  the 
many  short-branched  gills,  that  cover  the  aboral  surface  be- 
tween the  spines  like  the  pile  of  a  soft  mat.  The  gills  open 
into  the  body-cavity  at  their  bases.  Carbon  dioxide  passes 
through  the  same  organs  which  bring  in  the  oxygen. 

The  diagram  shows  nine  bulb-like  organs  on  the  outer 
margin  of  the  ring-canal.  These  are  called  the  Polian  vesicles 
(Fig.  120,  p).  The  small  glandular  bodies,  Tiedemanns  vesi- 
cles (Fig.  120,  £),  which  join  the  Polian  vesicles  are  thought 
to  have  the  function  of  producing  amoebocyte-cells,  described 
on  page  207.  The  cells  on  escaping  into  the  body-cavity 
consume  the  waste  substance  of  metabolism,  and  make  their 
way  through  the  body-wall,  perishing  on  the  outside.  Asterias 
has  no  definite  organs  of  excretion,  like  kidneys  or  nephridia. 

The  Nervous  System.  If  an  observer  takes  a  live  starfish, 
and  parts  the  tube-feet  in  an  arm  so  that  the  animal's  skin  is 
exposed  between  the  second  and  third  of  the  four  rows,  he 
may  see  the  dead- white,  radial  nerve-cord  extending  along  just 
beneath  the  skin  (Fig.  121,  17).  Fig.  120  shows  the  position 
of  the  nerve-ring  just  beneath  the  ring-canal.  The  circular 
blood-vessel  lies  between  the  ring-canal  and  the  nerve-ring. 

Reproduction  and  Development.  The  sexes  of  Asterias  vul- 
garis  are  separate,  but  externally  there  is  no  difference 
between  them.  At  the  time  the  dissections  were  made  for 
the  drawings,  the  sexual  glands  in  the  specimens  were  small 
(Fig.  119,  12;  Fig.  121,  18).  As  the  first  of  June  approaches, 
the  ten  sexual  glands  increase  in  size  until  they  occupy  all  the 
available  space  in  the  body-cavity  of  the  arms.  The  ovaries 
of  the  females,  when  they  contain  ripe  eggs,  are  bright  orange 
in  color  ;  the  spermaries  of  the  males  are  light  cream  color. 


244  GENERAL  ZOOLOGY 

From  about  the  first  to  the  middle  of  July,  in  the  latitude  of 
Boston,  the  sexual  cells  are  sent  out  into  the  water  through 
ten  small  holes  on  the  aboral  surface,  two  at  each  angle 
between  the  arms  all  around.  The  egg-cells  are  fertilized  by 
the  sperm-cells  in  the  water,  and  within  a  few  hours  the 
young  starfish  in  the  Uastula  stage  (see  p.  214)  is  swimming 
about  at  the  surface  by  the  aid  of  cilia.  The  manner  of 
development  after  the  yastrula  stage  (see  p.  215)  is  quite 
different  from  the  plan  described  for  the  earthworm.  The 
most  striking  incident  in  the  development  of  a  starfish  is  the 
change  that  takes  place  after  about  three  weeks  of  life  as  a 
pelagic  bilaterally  symmetrical  larva,  when  it  settles  toward 
the  bottom  and  fastens  temporarily  to  a  seaweed.  On  the 
posterior  region  a  star-shaped  bud  is  formed,  which  becomes 
the  adult  starfish.  As  the  bud  grows  it  draws  into  itself  the 
larva  which  gave  rise  to  it.  The  starfish  attains  the  stage  of 
sexual  maturity  within  a  year. 

Regeneration.  It  is  not  unusual  to  find  in  a  lot  of  star- 
fishes dredged  from  the  bottom,  many  specimens  that  have 
one  or  more  arms  shorter  than  the  others  (Fig.  119,  15). 
This  means  that  some  accident  has  befallen  the  irregular 
specimens,  and  that  new  arms  are  being  formed  to  take 
the  place  of  those  that  were  lost.  It  has  been  found  that  a 
starfish  deprived  of  all  its  arms  will,  under  favorable  circum- 
stances, reform  all  five ;  but  one  that  has  suffered  an  injury 
as  extensive  as  a  cut  through  the  entire  disk  probably  never 
survives. 

THE  BASKET-FISH 

Occasionally  fishermen  bring  up  on  their  hooks  from  the 
deep  waters  of  sounds  specimens  of  the  basket-fish,  Astroph'- 
yton  agassiz'ii  (Fig.  122).  It  is  very  difficult  to  keep  them 
alive  long  on  account  of  the  change  from  the  great  pressure 
and  the  low  temperature  of  their  habitat. 


THE  STARFISH  AND   SOME  ALLIES  245 

The  central  disk  is  more  distinct  in  the  basket-fish  than  in 
the  starfish.  The  five  arms,  instead  of  being  single,  divide 
and  redivide  many  times.  The  sieve-plate  lies  on  the  oral 
surface.  There  is  only  one  opening  to  the  .digestive  system, 
the  mouth.  The  tube-feet  do  not  extend  to  the  outside, 
hence  they  are  not  used  for  locomotion,  that  activity  being 
accomplished  by  the  branched  arms,  controlled  inside  by  mus- 
cles. Respiration  takes  place  through  little  pockets  which 
open  into  the  central  disk  from  below. 

Only  in  the  rarest  instances  is  it  possible  to  learn  anything 
of  the  activities  of  the  basket-fish.  Mr.  A.  Agassiz  and  Mrs. 
E.  C.  Agassiz  give  an  interesting  account  of  it  in  Seaside 


ni.  122.   Photograph  of  Basket-Fish,     x  \ 


246 


GENERAL  ZOOLOGY 


Studies  in  Natural  History.     They  say:   "  In  moving,  the  ani- 
mal lifts  itself  on  the  extreme  end  of  these  branches,  standing, 

as  it  were,  on  tiptoe,  so  that  the 
ramifications  of  the  arms  form  a 
kind  of  trelliswork  all  around  it, 
reaching  to  the  ground,  while  the 
disk  forms  a  roof.  In  this  living 
house  with  latticed  walls  small 
fishes  and  other  animals  are  occa- 
sionally seen  to  take  shelter ;  but 
woe  to  the  little  shrimp  or  fish 
who  seeks  a  refuge  there,  if  he  be 
of  such  a  size  as  to  offer  his  host 
a  tempting  mouthful ;  he  will  fare 
as  did  the  fly  who  accepted  the 
invitation  of  the  spider." 

THE  SEA-LILY 

At  the  present  day  we  find  here 
and  there  in  the  comparatively 
warm,  deep  waters  of  the  ocean, 
animals  like  that  shown  in  Fig. 
123  (Pentacri'nus  bla'kei).  In 
past  geological  eras  the  class  -to 
which  the  sea-lily  belongs  was  far 
more  widely  distributed  than  it 
is  now.  Members  of  the  genus 
Pentacrinus  may  be  obtained  by 
dredging  in  the  deep  waters  about 
Porto  Rico,  and  in  the  South 
Pacific  and  the  Indian  oceans. 
The  sea-lily  is  a  relative  of  the  starfish  and  the  basket-fish. 
The  central  disk  and  the  radial  arrangement  of  the  arms  make 


FIG.  123.   Sea-Lily.    Reduced 
(From  Report  of  H.  M.  S.  Challenger) 


THE  STARFISH  AND   SOME  ALLIES  247 

the  resemblance  striking.  In  Pentacrinus  blakei  the  number 
of  arms  varies ;  it  may  be  as  great  as  twenty.  The  sea-lily 
is  different  from  the  starfish  and  the  basket-fish,  in  having  a 
long  stalk  which  grows  from  the  center  of  the  aboral  surface 
and  sends  root-like  branches  in  among  the  rocks  at  the  bottom. 
The  mouth  and  the  arms  lie  on  the  oral  surface,  which  is 
uppermost.  A  water-vascular  system  is  present,  but  it  is  of 
no  service  to  the  animal  in  locomotion. 

Movement  in  Pentacrinus  is  limited  to  the  arms.  A  related 
genus,  Comat'ulus,  found  off  the  North  Atlantic  coast,  is  fixed 
by  a  stalk  when  young,  and  free  in  its  adult  stage,  moving 
about  then  like  a  basket-fish.  Food  is  brought  to  the  mouth 
of  Pentacrinus  by  the  wave-like  action  of  cilia  on  the  inner 
edge  of  all  the  arms. 

THE  SEA-URCHIN 

Practically  any  tide-pool  along  the  North  Atlantic  coast  that 
affords  specimens  of  starfish  will  harbor  several  sea-urchins. 
The  geographical  distribution  of  the  species  Strongylocentro'- 
tus  drobachien'sis  (Fig.  124)  is  very  wide.  It  is  found  on  the 
coast  of  Great  Britain  and  Norway,  along  the  North  Atlan- 
tic coast,  and  also  on  the  North  Pacific  coast,  —  in  all  these 
regions  from  tide-water  down  to  several  hundred  fathoms. 

Deprived  of  its  spines  a  sea-urchin  suggests,  as  Professor 
W.  F.  Ganong  aptly  says,  "  an  old-fashioned  door-knob."  It  is 
flattened  on  the  oral  surface  and  curved  above  into  a  rounded 
dome.  From  the  center  of  the  dome  one  may  trace  downward 
twenty  radiating  rows  of  calcareous  plates,  fitting  against  one 
another  closely.  Five  pairs  of  these  plates  radiating  at  equal 
angles  have  many  fine  holes  for  the  tube-feet ;  five  other 
pairs  of  plates  lie  in  the  spaces  between  the  regions  of  tube- 
feet.  All  over  the  aboral  surface  and  over  most  of  the  oral 
surface,  the  plates  bear  short,  rounded  knobs  on  which  the 


248 


GENERAL  ZOOLOGY 


spines  fit,  and  form  a  ball-and-socket  joint.  On  each  tube- 
foot  area  at  the  point  nearest  the  center  of  the  aboral  surface 
lies  an  eye ;  and  between  every  two  eyes  there  is  an  opening 
for  the  eggs,  or  spermatozoa,  to  emerge.  A  sieve-plate  lies 
in  one  of  the  spaces  between  two  eyes.  The  mouth  has  five 
sharp  teeth  which  meet  together  in  a  point.  The  breathing 
organs  are  located  on  the  oral  surface  around  the  mouth. 

Considering  the 
structure  of  the 
animal,  one  could 
be  almost  posi- 
tive that  the  sea- 
urchin  does  not 
get  its  food  after 
the  manner  of  the 
starfish.  It  feeds 
on  both  animal 
and  plant  sub- 
stance. Small  ani- 
mals are  captured 
by  the  tube-feet. 
The  tube-feet  may 
be  extended  to  a 
distance  equal  to 
half  the  diameter 
of  the  body ;  they 
affix  by  the  sucking-disk  to  some  small  creature  and  draw  it 
to  the  mouth.  All  food  is  then  ground  into  bits  by  the  five 
sharp  teeth  before  being  swallowed. 

A  sea-urchin  when  taken  from  the  water  and  placed  in  a 
person's  hand  causes  a  gentle  tickling  of  the  skin.  This 
it  does  with  its  movable  spir>es.  The  spines  may  be  of  use 
as  levers  in  pushing  the  body  along,  but  locomotion  in  a 
definite  direction  is  accomplished  by  the  tube-feet  on  the 


FIG.  124.    Photograph  of  Sea-Urchin.     Slightly 
reduced 


THE  STARFISH  AND  SOME  ALLIES  249 

oral  surface,  aided  by  some  of  those  on  the  aboral  surface, 
all  extending  and  contracting  much  as  in  the  starfish.  The 
uppermost  tube-feet  are  used  as  tentacles  for  feeling,  and  it 
may  be  for  smelling  also.  The  fact  that  sea-urchins  collect 
in  numbers  about  the  body  of  a  large  dead  animal  in  the 
water,  indicates  that  they  have  the  sense  of  smell. 

In  certain  parts  of  our  eastern  coast,  members  of  the  genus 
Strongylocentrotus  live  in  cavities  in  the  rock,  which  are 
excavated  by  the  animals  themselves.  A  related  species  living 
on  the  coast  of  California  burrows  a  hole  in  the  solid  rock  deep 
enough  to  conceal  itself  entirely.  No  one  knows  positively 
how  the  burrowing  is  done.  Probably  three  factors  take  part 
to  a  varying  degree,  —  gnawing  by  the  teeth,  slow  grinding 
by  voluntary  movement  of  the  spines,  and  incessant  slight 
turnings  of  the  whole  body  by  the  waves. 

THE  SEA-CUCUMBER 

Sea-cucumbers  of  various  species  are  found  in  every  ocean. 
The  species  represented  in  Fig.  125  (Cucuma'ria  chronhjel'mi) 
is  found  in  Puget  Sound,  Washington.  It  lives  on  the 
bottom. 

The  animals  are  about  four  inches  long.  The  body  is  cylin- 
drical, but  without  calcareous  plates  that  touch  one  another 
and  keep  the  form  constant.  The  only  trace  of  a  skeleton 
comparable  to  that  of  the  sea-urchin  consists  of  scattered  bits 
of  calcareous  secretions  of  definite  form  beneath  the  skin.  Al- 
though the  sea-cucumber  is  radially  symmetrical,  having  the 
five  double  rows  of  tube-feet  along  the  cylinder,  we  can  speak 
of  the  anterior  and  posterior  ends,  because  the  animal  lies  flat. 

The  anterior  region  is  the  oral  region.  At  the  centej;  we 
observe  the  round  mouth,  about  which  are  the  ten  branching 
tentacles.  Internally  there  is  a  water-vascular  system  with 
a  ring-canal  and  radial  canals.  In  respiration  water  is  drawn 


250  GENERAL  ZOOLOGY 

into  the  intestine  at  the  aboral  end,  and  an  exchange  of  gases 
takes  place  through  internal  gills  that  join  the  intestine. 

The  tentacles  in  the  picture  are  not  extended  in  the  usual 
radial  direction.    The  reason  is  that  when  photographed  the 


LA 

•,  A 


T* 


FIG.  125.  Photograph  of  Living  Sea-Cucumber.    Natural  size 

animal  was  using  its  tentacles  as  well  as  its  tube-feet  to  crawl 
along  the  bottom  of  a  dish  of  sea-water.  When  the  animal  is 
at  rest,  the  tentacles  are  probably  used  to  capture  small 
animals,  and  to  pass  them  to  the  mouth. 

Relatives   of  Cucumaria  have  been   known  by  observers 
to  disgorge   the   entire  set  of  internal  organs  through   the 


THE   STARFISH  AND   SOME  ALLIES  251 

mouth-opening.  In  captivity  they  appear  to  do  this  when 
placed  in  unfavorable  situations.  It  is  not  so  remarkable  that 
they  should  lose  their  internal  organs,  as  it  is  that  they  should 
regenerate  them  all  again  as  perfect  as  ever.  If  sea-cucum- 
bers throw  out  their  internal  organs  in  nature,  it  would 
appear  to  be  a  very  expensive  process.  Since  they  do  per- 
form this  action,  in  nature  as  well  as  in  captivity,  there  must 
be  some  reason  for  it.  The  only  reason  that  suggests  itself  is 
based  on  the  fact  that  fish  prey  upon  sea-cucumbers.  The 
sea-cucumber  is  a  slow-moving  animal,  and  once  seen  by  a 
roving  fish  the  chances  of  escape  under  ordinary  circumstances 
would  be  few  indeed.  If  the  prospective  victim  when  dis- 
turbed were  to  eject  its  internal  organs  into  the  water,  the 
fish,  true  to  the  instinct  of  its  kind,  would  gobble  up  the 
swiftly  moving  object,  and  probably  go  away  satisfied. 

Sea-cucumbers  are  prepared  and  used  as  food  by  the  Chinese, 
and  it  is  reported  that  the  Siwash  Indians  of  the  northwest 
of  the  United  States  eat  them,  and  sea-urchins  also. 


DEFINITION  OF  ECHINODERMA 

Each  of  the  five  animals  described  in  this  chapter  represents 
one  of  the  five  classes  that  make  up  the  phylum  Echino- 
der'ma  (Gr.  ecliinos,  hedgehog ;  derma,  skin).  The  five  classes 
represented  are  Asteroi'dea,  by  Asterias;  Ophiuroi' dea,  by 
Astrophyton;  Crinoi'dea,  by  Pentacrinus ;  Uchinoi'dea,  by 
Strongylocentrotus ;  and  Holothuroi'dea,  by  Cucumaria. 

The  most  important  characteristics  of  the  phylum  are  the 
radial  symmetry  of  the  body  (the  importance  of  this  character 
is  denied  by  some  zoologists);  the  occurrence  of  repeated 
divisions  or  organs  of  the  body  to  the  number  of  five,  or 
in  multiples  of  five ;  and  the  existence  of  a  water-vascular 
system.  No  other  phylum  has  parts  occurring  in  fives,  and 
none  other  has  a  water-vascular  system. 


CHAPTER  XIX 
THE  SEA- ANEMONE  AND  SOME  ALLIES:   OELENTERA 

To-day  the  many-hued  anemone 
Waving,  expands  within  the  rock-pools  green, 
And  swift,  transparent  creatures  of  the  sea 
Dart  throu'  the  feathery  sea-fronds  scarcely  seen. 

SIR  LEWIS  MORRIS. 

The  Sea-Anemone.  The  best-known  sea-anemone  of  the 
North  Atlantic  coast  is  Metrid'ium  margina'tum  (Figs.  126, 
128,  and  129).  Although  this  species  is  usually  found  in  tide- 
pools,  it  also  lives  attached  to  the  piles  of  wharves  in  har- 
bors where  the  impurities  of  the  water  are  not  too  great. 
The  picture  of  the  tide-pool  shows  sea-anemones  in  various 
attitudes.  Metridium  has  the  power  of  moving,  by  creeping 
along  on  its  base,  but  it  seldom  changes  its  place  of  attach- 
ment, even  in  the  coldest  weather. 

The  form  of  Metridium  is  nearly  cylindrical.  The  base, 
which  is  the  aboral  surface  of  the  animal,  widens  irregularly 
to  fit  the  surface  of  attachment,  thus  enabling  the  body  to 
maintain  its  hold  by  expelling  the  water  from  beneath  the 
disk.  The  oral  end  of  the  column-shaped  body  expands  into 
a  crown  of  many  small,  slender  tentacles.  At  the  middle  of 
the  oral  surface  is  the  mouth.  The  skin  of  the  body  is  soft, 
but  rather  tough.  An  animal  with  the  general  plan  of  struc- 
ture of.  the  sea-anemone  is  called  &  polyp.. 

The  food  of  the  sea-anemone  consists  in  general  of  many 
kinds  of  microscopic  pelagic  organisms.  The  capture  of 
prey  is  accomplished  by  a  method  peculiar  to  the  phylum  to 
which  Metridium  belongs.  All  over  the  tentacles  are  number- 
less microscopic  cells  containing  nettling -capsules  (compare 

252 


FIG.  126.  Tide-Pool  Study  of  Sea-Anemones,  East  Point,  Nahant,  Mass. 

253 


254 


GENERAL  ZOOLOGY 


Fig.  127,  Hy'dra,  see  p.  263).  When  any  small  animal  strikes 
against  the  minute  bristle  (Fig.  127,  A,  3)  that  arises  from  the 
external  surface  of  one  of  these  cells,  the 
capsule  breaks,  and  a  slender,  hollow 
thread  or  filament  (Fig.  127,  B,  4)  shoots 
out;  reversing  itself  from  the  base,  like 
the  pharynx  of  the  sand  worm,  and  pierces 
the  skin  of  the  creature.  In  the  capsule 
there  is  some  fluid  which  is  discharged 
through  the  filament  and  poured  into  the 
wound.  The  effect  of  the  fluid  is  to  be- 
numb the  victim. 

A  sea-anemoHe  resting  in  the  attitude 
of  the  one  shown  in  Fig.  128  could  not 
swallow  anything,  even  after  the  victim 
had  been  overcome.  The  reason  is  that 
the  minute  cilia  which  cover  the  tentacles 
wave  outward  at  all  times.  As  long  as 
particles  of  wasfe  and  other  undesirable 

FIG.  127.   Nettle-Cells     substances  fall  within  range  of  the  cilia, 
of  Hydra.    Much,!  ,-,1  -,  •> 

enlarged.   (After     they  are  swept  out  of  the  way  ;  but  when- 


ever small  animals  come  within  range  of 
the  cilia,  and  are  paralyzed  by  the  net- 
tling filaments,  the  tentacles  bend  over 
with  their  tips  pointing  toward  the 
mouth.  The  normal  action  of  the  cilia 


Schneider) 

A,  nettle-cell,  with  un- 
discharged nettling 
capsule;  B,  nettle- 
cell,  with  discharged 
nettling  capsule  : 

1,  nettling  capsule  ; 

2,  nucleus  of  nettle-     now  sweeps  the  helpless  creatures  toward 
cell:  3,  bristle  of      ,!  ,  ,1         A  -n  ,-, 
nettle-cell ;  4,  hollow     the  sea-anemone  s  mouth.    All  over  the 

filament  of  nettling     thick,  grooved  lip  there  are  more  cilia. 
The   cilia  at  the  opposite  ends  of  the 

mouth  lie  in  a  deep,  wide  groove  called  the  sipTionoglyphe 
(Fig.  129,  3).  Here  the  cilia  always  wave  inward.  At  the 
sides  of  the  mouth  the  cilia  wave  outward  except  when  food 
is  dropped  on  them  by  the  cilia  of  the  tentacles ;  then  they 


THE  SEA-ANEMONE  AND   SOME  ALLIES        255 


reverse  their  action,  and  all  the  mouth-cilia  unite  in  sweeping 
the  food  down  the  gullet.  These  observations  were  made  by 
Professor  G.  H.  Parker,  of  Harvard  University,  in  1896. 

The  mouth  opens  to  receive  the  food,  which  is  sometimes 
quite  large,  and  the  gullet  (Fig.  129,  4)  passes  it  down  by 
ciliary  action  aided  by  muscular  activity  in  the  gullet-wall. 


FIG.  128.  Photograph  of  Living  Sea-Anemone.    Natural  size 

At  the  inner  end  (Fig.  129,  5)  of  the  gullet,  food  passes  into 
a  large  space  which  extends  radially  between  mesenteries  (par- 
titions) (Fig.  129,  12,  13)  to  the  body- wall.  Thus  there  is  no 
distinct  alimentary  canal  separate  from  a  body-cavity.  This 
fact  shows  the  sea-anemone  to  be  a  less  specialized  animal, 
and  hence  a  lower  form,  than  any  we  have  yet  studied.  Those 


256 


GENERAL  ZOOLOGY 


animals  that  do  not  have  a  body-cavity  and  an  alimentary 
canal  have  but  one  cavity  to  take  their  place ;  this  cavity  is 


FIG.  129.  Dissection  of  the  Sea-Anemone  (Metridium  marginatum). 
Natural  size 

1,  intermediate  zone;  2,  lip;  3,  siphonoglyphe ;  4,  gullet;  5,  inner  end  of  gullet; 
6,  edge  of  mesentery ;  7,  cavity  of  a  tentacle ;  8,  inner  ostium ;  9,  outer  ostium ; 
10,  primary  mesentery;  11,  muscle-plate  on  primary  mesentery;  12,  abnor- 
mal tertiary  mesentery ;  13,  secondary  mesentery ,-  14,  tertiary  mesentery ; 
15,  quaternary  mesentery;  16,  reproductive  gland;  17,  mesenterial  filament; 
18,  opening  for  mesenterial  filament. 

called  the  gastrovascular  cavity,  because  in  the  same  space 
food  is  digested  and  carried  about.  The  fact  that  food  and 
oxygen  can  pass  into  any  portion  of  the  body,  even  into 


THE  SEA-ANEMONE  AND   SOME  ALLIES        257 

ollow  tentacles  (Fig.  129,  7),  accounts  for  the  absence  of  a 
circulatory  system,  which  usually  serves  the  purpose  of  trans- 
porting oxygen,  digested  food,  and  also  waste  products  from 
part  to  part  in  the  animal  body.  Likewise  we  find  no  gills 
or  nephridia,  for  probably  all  the  waste  products  of  metab- 
olism are  sent  from  the  cells  into  the  gastrovascular  cavity 
and  ultimately  to  the  outside.  The  absence  of  all  these  spe- 
cial organs  is  further  indication  of  a  low  and  simple  type  of 
organism. 

There  are  usually  six  pairs  of  principal  mesenteries  in 
Metridium  marginatum.  They  are  thin,  radial  partitions 
extending  from  the  gullet  outward  and  downward  to  the 
body-wall.  These  six  pairs  are  called  the  primary  mesen- 
teries (Fig.  129,  10,  11).  In  the  arcs  between  the  sets  of  pri- 
mary mesenteries  there  are  secondary  mesenteries,  also  in 
pairs  (Fig.  129,  13),  arising  from  the  body-wall  and  extend- 
ing part  way  toward  the  gullet.  The  tertiary  mesenteries 
(Fig.  129,  14)  and  the  quaternary  mesenteries  (Fig.  129,  15) 
extend  shorter  distances  into  the  gastrovascular  cavity,  but  all 
unite  with  the  body-wall  of  the  oral  and  the  aboral  ends,  and 
in  the  latter  place  meet  at  the  center.  Occasionally  a  mesen- 
tery grows  beyond  the  usual  width  and  becomes  attached  to 
the  gullet,  as  in  Fig.  129,  12.  Every  mesentery  has  a  longitu- 
dinal muscle-band  (Fig.  129,  11)  on  one  side  near  its  free  or 
inner  edge.  In  all  but  two  pairs  of  mesenteries  the  muscle- 
bands  face  each  other.  The  four  primary  mesenteries  which 
are  directed  toward  the  siphonoglyphes  have  their  muscle- 
bands  on  the  outside.  At  the  oral  end  there  are  two  circles 
of  openings  called  ostia  (Fig.  129,  8,  9).  They  perforate  all 
the  primary  mesenteries  and  bring  the  radial  chambers  into 
communication  at  that  end. 

At  the  free  edge  of  the  widest  mesenteries  below  the  end 
of  the  gullet  there  are  to  be  found  coiled  masses  which  are 
composed  chiefly  of  mesenterial  filaments  (Fig.  129,  17, 18). 


258  GENERAL  ZOOLOGY 

These  filaments  are  thickly  set  with  microscopic  nettle-cells, 
like  those  shown  in  Fig.  127.  When  the  animal  is  dis- 
turbed greatly,  the  mesenterial  filaments  stream  out  through 
the  mouth  and  through  small  invisible  openings  in  the  body- 
wall.  It  is  likely  that  the  most  frequent  use  of  the  mesen- 
terial filaments  is  in  defense. 

The  egg-cells  and  the  sperm-cells  of  Metridium  are  found 
in  separate  individuals,  and  adjacent  to  the  mesenterial  fila- 
ments (Fig.  129,  16).  The  development  of  Metridium  has  not 
been  studied,  but  in  kindred  species  embryologists  have  found 
that  the  eggs  are  fertilized  while  they  are  still  in  the  mes- 
enteries. At  a  certain  stage  of  development  the  embryo  is 
freed.  It  passes  out  through  the  mouth  of  the  female,  swims 
awhile  by  cilia,  and  finally  settles  and  continues  life  after 
the  manner  of  the  adult.  Reproduction  takes  place  probably 
most  frequently  by  budding  (the  formation  of  small  individ- 
uals on  the  edge  of  the  aboral  surface),  and,  rarely,  by  longi- 
tudinal division  into  halves. 

Wherever  the  sea-anemone  lives,  in  tide-pools,  on  piles  of 
wharves,  on  rubble  beaches,  or  in  the  deeper  waters  of  bays, 
it  has  to  contend  with  whatever  unfavorable  conditions  char- 
acterize the  place.  The  periodic  fall  of  the  tide  leaves  some 
individuals  exposed  to  the  drying  effect  of  the  air.  They  meet 
the  conditions  by  contracting  the  organs  of  the  oral  end,  and 
exposing  as  little  surface  as  possible  to  the  air  (Fig.  126). 
On  account  of  their  tough  skin,  their  nettle-cells,  and  their 
ability  to  hold  to  a  fixed  support,  it  is  not  likely  that  adult  sea- 
anemones  are  ever  attacked  by  fishes  or  other  ravenous  animals. 
We  cannot  tell  how  many  of  the  pelagic  young  sea-anemones 
are  lost  by  being  swept  upon  the  beach,  or  how  many  are  car- 
ried far  out  into  the  ocean,  or  swallowed  by  larger  animals. 
Undoubtedly  the  number  is  very  great. 

The  protection  insured  to  the  adult  sea-anemone  by  its 
tough  skin  and  its  nettle-cells  is  considerable,  and  we  find  no 


THE  SEA-ANEMONE  AND  SOME  ALLIES        259 

relation  between  the  color  of  the  animal  and  the  c'olor  of  the 
objects  in  the  environment.  In  the  same  situation  one  may 
find  all  variations  of  uniform  or  mingled  shades,  from  light 
yellow  to  dark  brown,  —  a  fact  which  of  itself  would  indicate 
that  the  animal  does  not  depend  on  color-resemblance  for 
protection. 

The  Coral  Polyp.  The  only  coral  polyp  of  the  North 
Atlantic  coast  is  Astran'gia  da'nce  (Fig.  130).  It  occurs  in 
colonies  of  many  individuals  and  incrusts  rocks  or  pebbles 


FIG.  130.  Colony  of  Coral  Polyps.    Enlarged 

in  shallow  water,  near  the  shore  line  from  Massachusetts  to 
North  Carolina. 

A  polyp  of  Astrangia  is  about  one  eighth  of  an  inch  in 
diameter  and  of  variable  length.  It  bears  a  very  obvious 
resemblance  to  a  sea-anemone.  The  columnar  form,  the  flat- 
tened aboral  surface  resting  on  a  support,  and  the  oral  end 
with  its  crown  of  tentacles,  prove  the  relationship.  Besides, 
examination  of  the  interior  reveals  the  presence  of  mesenteries 
arranged  very  much  as  in  Metridium.  One  important  struc- 
ture of  Astrangia,  however,  is  never  found  in  the  sea-anemone, 
and  that  is  the  carbonate  of  lime  "  skeleton."  This  structure 


260  GENERAL  ZOOLOGY 

at  the  base  of  the  polyp  is  more  definitely  referred  to  under 
the  name  corallite,  for  it  is  not  a  true  skeleton.  Several  coral- 
lites  are  shown  in  the  lower  portion  of  the  figure.  The  hard, 
radial  plates  repeat  the  number  of  pairs  of  mesenteries  of  the 
polyp,  since  each  plate  is  formed  between  the  members  of 
pairs  of  mesenteries. 

The  aboral  surface  of  the  polyp  is  molded  over  the  corallite 
so  that  the  soft  tissue  of  the  animal  extends  down  between 
the  radial  plates,  and  also  over  the  circumference.  Although 
the  polyp  may  be  said  to  fit  into  the  corallite,  it  is  the  real 
cause  of  the  existence  of  the  corallite. 

The  substance  of  the  corallite  is  formed  by  the  crystalli- 
zation of  carbonate  of  lime  in  the  epidermal  cells  of  the  polyp. 
Crystallization  takes  place  in  the  outermost  cells,  and  as  the 
substance  in  them  hardens  newer  cells  are  formed  just  within, 
and  in  these  the  process  of  crystallization  continues.  Thus  it 
is  that  as  the  coral  polyp  grows,  it  actually  pushes  itself  far- 
ther and  farther  away  from  the  surface  to  which  it  became 
attached  at  the  beginning  of  its  fixed  life.  Astrangia  has  a 
characteristic  method  of  forming  a  colony.  The  height  of  a 
corallite  does  not  exceed  a  half-inch.  The  colony  increases 
by  budding  from  the  older  polyps  at  their  bases.  The  result 
is  a  low  mass  of  corallites  that  seldom  exceeds  an  area  of  four 
inches  square. 

Definition  of  Actinozoa  (Gr.  aktis  (aktiri),  ray ;  zoon,  ani- 
mal). The  members  of  the  class  Actinozo'a  are  alike  in  having 
a  soft,  generally  cylindrical  body.  The  plan  of  structure  is 
bilaterally  symmetrical,  as  indicated  in  the  arrangement  of 
mesenteries  in  the  gastrovascular  cavity,  it  being  possible  to 
pass  a  line  lengthwise  through  the  mouth  to  opposite  siphono- 
glyphes,  and  separate  one  half  the  mesenteries  from  the  other 
half.  Superficially,  however,  as  indicated  by  the  arrangement 
of  the  tentacles,  there  is  radial  symmetry.  Into  the  single, 
partially  divided  gastrovascular  cavity  the  mouth  opens,  and 


THE  SEA-ANEMONE  AND  SOME  ALLIES        261 

through  it  food  enters  and  unused  particles  are  discharged. 
Nettling-capsules,  which  are  the  organs  of  offense  and  defense, 
are  at  the  surface  of  the  tentacles  and  on  the  mesenterial 
filaments. 

Coral  Islands.  Ever  since  Charles  Darwin  from  1831  to 
1836  made  his  famous  journey  around  the  world  in  H.M.S. 
Beagle,  scientific  explorers  have  engaged  from  time  to  time 
in  the  study  of  the  life  and  structure  of  coral  reefs  and 
islands.  We  know  from  their  researches  that  coral  reefs  are 
formed  of  great  masses  of  carbonate  of  lime,  largely  as  the 
result  of  the  secretion  of  that  substance  by  polyps. 

Just  as  with  other  organisms,  reef-forming  polyps  flour- 
ish wherever  they  become  adapted  to  external  conditions. 
The  food  they  need  is  probably  abundant  anywhere  in  the 
seas,  but  they  cannot  endure  the  temperature  common  to 
regions  outside  the  torrid  zone.  They  can  live  in  situations 
where  the  tide  recedes  from  them  for  two  or  three  hours, 
or  in  depths  as  great  as  fifty  fathoms  (300  feet),  but  the  most 
general  limit  of  depth  for  the  greatest  number  of  species  is 
about  twenty  fathoms.  A  condition  which  checks  their  dis- 
tribution near  large  bodies  of  land  is  the  presence  of  silt,  as 
in  the  fresh  water  that  flows  from  the  mouths  of  rivers. 
Fresh  water  itself  when  free  from  impurities  is  not  especially 
detrimental  to  the  growth  of  coral  polyps.  The  most  famous 
coral  formations  are  found  in  the  region  of  the  Bahama  Islands, 
in  the  Great  Barrier  Reef  of  Australia,  in  the  Fiji  Islands  of 
the  South  Pacific  Ocean,  and  in  the  Maldive  Islands  of  the 
Indian  Ocean. 

When  conditions  permit,  young  coral  polyps  attach  them- 
selves to  the  sea-bottom  near  a  body  of  land,  and  by  the 
process  of  secreting  carbonate  of  lime,  as  described  for 
Astrangia,  extend  upward  toward  the  surface  in  the  form  of 
a  long,  narrow  ridge  skirting  the  land.  When  the  ridge  is 
so  near  the  land  that  it  leaves  no  channel,  it  is  called  a 


262  GENERAL  ZOOLOGY 

fringing  reef.  If  by  subsequent  changes,  or  as  originally 
formed,  a  navigable  channel  lies  between  the  ridge  and  the 
land,  it  is  called  a  barrier  reef.  If  the  formation  surrounds 
a  body  of  water,  which  it  nearly  or  completely  cuts  off  from 
the  sea,  it  is  .called  an  atoll.  The  most  remarkable  examples 
of  atolls  are  the  Maldive  Islands. 

Two  important  theories  have  been  advanced  to  account 
for  the  historical  connection  which  in  many  cases  is  thought 
to  exist  between  fringing  reefs,  barrier  reefs,  and  atolls. 
Darwin  believed  that  an  atoll  begins  as  a  fringing  reef  sur- 
rounding an  oceanic  island,  which  may  be  of  volcanic  or  other 
origin,  and  that  as  the  island  sinks  from  internal  causes,  the 
coral  polyps  build  up  carbonate  of  lime  as  long  as  they  are 
within  their  range  of  favorable  depth.  The  reef  that  at  first 
was  a  fringing  reef  becomes  a  barrier  reef,  on  account  of  the 
increase  in  distance  between  it  and  the  decreasing  area  of 
sinking  land.  At  last  the  top  of  the  island  disappears  beneath 
the  water,  and  the  atoll  remains.  Professor  J.  D.  Dana,  and 
others,  have  published  evidence  in  support  of  Darwin's  sub- 
sidence theory,  but  the  erosion  theory  suggested  by  Dr.  John 
Murray,  leader  of  the  exploring  expedition  of  H.M.S. 
Challenger  (1850),  has  probably  more  adherents  at  the  present 
day.  The  erosion  theory  has  been  modified  and  extended, 
chiefly  by  Dr.  Alexander  Agassiz.  According  to  this  theory 
coral  polyps  may  form  a  fringing  reef  about  an  oceanic  island. 
The  reef  continues  to  grow,  while  the  soil  or  rock  of  the 
island  is  carried  away  by  rains  and  by  rivers.  The  solution  of 
the  soil  and  rock  is  caused  by  the  temporary  chemical  union 
of  these  substances  with  carbon  dioxide  derived  from  dead 
animals  and  plants.  The  idea  is  that  in  the  course  of  a  few 
centuries  an  entire  island  could  be  worn  away,  and  the  atoll 
left  with  its  lagoon  of  Avater  partially  connected  with  the  sea. 

Dr.  Murray  suggested  also  the  probability  of  atolls  being 
formed  without  the  preliminary  stages  of  fringing  and  barrier 


THE  SEA-ANEMONE  AND  SOME  ALLIES       263 

reefs.  If  coral  polyps  were  to  attach  to  a  submerged  plateau 
not  too  deep  for  them  to  live  on,  the  small  colony  would  grow 
upward  and  extend  itself  radially,  something  like  the  flaring 
sides  of  a  shallow  wash-basin.  As  the  mass  grows  larger  the 
polyps  at  the  center  would  be  killed  by  the  detritus  collecting 
from  the  broken  pieces  of-  coral  rock  at  the  wave-beaten 
margin,  and  the  rock  already  formed  at  the  center  would  be 
worn  and  scooped  out  by  erosion  with  coral  sand. 

Coral  atolls  are  imperishable  bulwarks  against  the  sea,  and 
in  some  cases  have  formed  the  beginning  of  strips  of  land 
sufficiently  wide  for  wild  races  of  men  to  live  upon. 

The  Fresh-Water  Polyp.  There  are  but  twro  species  of 
fresh- water  polyps  that  are  at  all  common,  and  these  are  so 
small  that  the  casual  observer  would  seldom  be  aware  of  their 
existence,  even  though  they  were  abundant  in  his  aquarium. 
The  two  species  are  Hy'dra  vir'idis  (Fig.  131),  the  green 
hydra,  and  Hydra  fus'ca,  the  brown  hydra. 

Hydra  viridis  lives  among  green  fresh-water  plants  in 
places  where  there  is  abundant  sunlight.  At  rest  it  holds  to 
a  plant  with  its  aboral  surface,  the  remainder  of  the  body 
floating  outward  or  downward  very  much  like  the  sea-anemone. 
The  body,  which,  is  cylindrical  in  form,  is  about  3  mm. 
(^  inch)  long  and  .4  mm.  (^  inch)  in  diameter.  A  little  prac- 
tice will  enable  a  person  to  distinguish  one  in  an  aquarium, 
for  specimens  frequently  leave  the  green  plants  and  crawl 
up  the  side  of  the  glass  nearest  the  light.  They  can  move 
either  by  a  slow,  creeping  movement  on  the  aboral  surface, 
or  by  the  process  of  "  looping,"  like  an  inchworm.  Hydras 
exist  for  a  long  time  in  an  aquarium,  provided  there  is  an 
abundance  of  their  food-animals,  which  are  usually  small 
Crustacea.  The  most  common  of  these  is  a  fresh-water  spe- 
cies of  Cyclops  (resembling  Fig.  75),  which  they  benumb 
with  their  nettling-threads,  and  carry  to  the  mouth  with  their 
tentacles. 


264 


GENERAL  ZOOLOGY 


The  number  of  tentacles  a  specimen  of  Hydra  viridis  may 
have  depends  upon  its  size,  and  also  upon  its  age.    The  small 

individuals  are  gener- 
ally the  youngest; 
these  have  four  tenta- 
cles. The  larger,  older 
ones  gain  in  the  num- 
ber of  tentacles,  up  to 
the  extreme  number  of 
eleven;  but  there  is  a 
greater  per  cent  of  in- 
dividuals with  six  ten- 
tacles than  with  any 
other  number. 

Internally,  Hydra  is 
the  simplest  animal 
we  have  studied.  The 
mouth  (Fig.  131,  1) 
opens  into  a  cylindrical 
cavity  (Fig.  131,  7)  with 
no  indication  of  gullet, 
or  radial  partitions. 

FIG.  131.   Fresh- Water  Polyp.    Longitudinal      The  cavity  extends  by 

slender  tubes  out  into 
each  tentacle,  and  in  all 

,gastrovascular  cavity ;  8,  spermatozoa  form-      parts    Only    two    layers 

of  cells  separate  it  from 
the  water  outside.  The 
inner  one  of  these  two  layers  is  the  endoderm  (Fig.  131,  6), 
and  the  outer  one,  the  ectoderm  (Fig.  131,  5).  Cells  of  the 
endoderm  secrete  fluid  for  digesting  food,  and  even  take  up 
small  particles  of  food,  digesting  them  inside  the  cell-sub- 
stance. The  ectodermal  cells  are  modified  into  nettle-cells, 
nerve-cells,  muscle-cells,  and  general  surface-cells. 


9 


section.    Much  enlarged 

1,  mouth;  2,  tentacle;  3,  forming  bud;  4,  older 
bud  ;  5,  ectodermal  cells ;  6,  endodermal  cells ; 


ing ;  9,  egg  forming 

(From  Parker's  Elementary  Rioloyy} 


THE  SEA-ANEMONE  AND   SOME  ALLIES        265 


-3 


Reproduction  may  take  place  by  the  sexual  method,  or  by 
budding.  Eggs  (Fig.  131,  9)  are  developed  in  the  ectoderm 
near  the  aboral  end.  In  the  same 
individual  spermatozoa  (Fig. 
131,  8)  are  formed  in  the  ectoderm 
nearer  the  oral  end,  and  these  on 
escaping  fertilize  the  eggs,  which 
remain  in  the  ectoderm  for  some 
time  as  embryos.  Then  the  em- 
bryos separate  from  the  parent, 
and  after  swimming  about  for  a 
variable  period  develop  into 
organisms  like  the  parent.  Non- 
sexual  reproduction  is  the  more 
frequent  method,  however.  Buds 
involving  both  ectoderm  and 
endoderm  form  on  the  side  of  the 
body  (Fig.  131,  3,  4) ;  four  tenta- 
cles appear,  the  mouth  forms,  and 
the  base  of  the  bud  constricts, 
setting  the  young  Hydra  free  to 
begin  its  own  career. 

Hydroids  and  Medusae.  There 
is  a  large  group  of  animals  closely 
allied  to  Hydra,  that  live  in  the 
sea.  A  portion  of  one  of  them, 
Bougainvitfliafrutieo'sa,  is  shown 
in  Fig.  132.  It  looks  very  much 
like  a  plant,  owing  to  its  habit  of 
branching.  The  colony  may  con- 
tain many  polyps,  each  of  which 

is  connected  indirectly  with  every  other  by  means  of  the 
continuous  body-wall.  At  the  base  of  the  colony,  root-like 
branches  from  a  stem-like  structure  cling  to  floating  timbers 


FIG.  132.    Hydroid.    Much  en- 
larged.   (After  Allman) 

1,  tentacles;  2,  3,  4,  stages  in  the 
formation  of  medusa 


266 


GENERAL  ZOOLOGY 


or  buoys.  Although  the  colony  reaches  the  height  of  two 
inches,  the  individual  polyps  are  microscopic  in  size.  Each 
polyp  has  about  fourteen  tentacles  amply  provided  with  net- 
tling capsules,  which  aid  in  capturing  small  pelagic  animals. 
The  mouth  is  at  the  center  of  the  circles  of  tentacles 
(Fig.  132,  l) ;  it  opens  directly  into  the  gastrovascular  cavity. 
As  the  branches  are  terminated  by  feeding  polyps,  the  cells 

of  the  branches  are  probably  supplied 
with  food  by  the  polyps  nearest  at 
hand. 

Reproduction  in  Bougainvillia  may 
be  a  mere  increase  in  the  number  of 
polyps  by  a  process  of  budding  similar 
to  that  described  for  Hydra.  Occa- 
2  sionally,  however,  a  bud  develops  into 
a  structure  totally  different  from  an 
ordinary  polyp,  and  after  a  series  of 
stages  indicated  in  Fig.  132,  2,  3,  4, 
finally  becomes  separated  from  the 
colony  and  floats  away  as  a  free- 
swim  mi  11  g  individual  (Fig.  133). 

FIG.  133.   Medusa.     Much      This    is    callecl    the    ^edltsa    stage    of 

enlarged.  (After  Allman)      the  animal.     The  medusa  has  some- 

i,  bell;  2,  tentacle;  .3,  maim-     thing  like  the  shape  of  an  umbrella. 

The  mouth  is  located  at  the  end  of 
the  pendent  manubrium  (Fig.  133,  3). 
The  gastrovascular  cavity  sends  out  four  slender  tubes  (Fig. 
133,  4)  radially  to  the  perimeter,  where  a  circular  canal  joins 
them.  Tentacles  (Fig.  133,  2)  stream  downward  from  the  mar- 
gin, and  at  their  bases  are  minute  sense-organs  (Fig.  133,  5). 
There  are  male  and  female  medusas.  The  ovaries  and  the 
spermaries  of  Bougainvillia  are  located  in  the  manubrium. 
When  the  eggs  and  spermatozoa  are  ripe,  they  pass  out 
through  the  mouth,  and  fertilization  takes  place  in  the  water 


brium;  4,  radial  tubes; 
5,  sense-organs 


THE  SEA-ANEMONE  AND   SOME  ALLIES       267 

outside.  The  embryo  swims  about  for  awhile  and  then  set- 
tles to  some  fixed  or  floating  object,  attaches  itself,  and  soon 
another  colony  of  the  hydroid  (hydra-like)  stage  is  developed 
by  budding.  The  life-history  of  Bougainvillia  illustrates 
alternation  of  generations.  The  fixed,  colonial,  non-sexual, 
hydroid  stage  alternates  with  the  free-swimming,  single, 
sexual,  medusa  stage,  and  together  they  complete  the  life- 
cycle. 

Definition  of  Hydrozoa  (Gr.  Hydra,  the  fabulous  monster; 
zoa,  animals).  The  class  Hydrozo'a  includes  the  genus  Hydra 
and  many  thousands  of  species  of  hydroids.  The  life-history 
described  for  Bougainvillia  by  no  means  applies  to  all  spe- 
cies of  hydroids,  but  it  is  as  characteristic  as  any.  Hydrozoa 
are  small  animals  occuring  singly  and  in  colonies.  There  is 
but  one  cavity  in  the  body,  and  that  is  continuous  with  the 
mouth-opening.  There  are  but  two  layers  of  cells,  the  ecto- 
derm and  the  endoderm.  In  some  members  of  the  class  the 
two  layers  are  separated  by  a  jelly-like  mass  secreted  by  the 
cells.  The  body  is  radially  symmetrical.  Tentacles  with  net- 
tling-capsules  in  their  ectodermal  cells  are  the  organs  of 
offense  and  defense. 

The  Jellyfish.  Although  the  name  "  jellyfish  "  is  sometimes 
applied  to  the  medusae  of  the  class  Hydrozoa,  it  is  more  com- 
monly given  to  the  larger,  saucer-shaped  or  bell-shaped  animals 
that  swim  at  or  near  the  surface  in  harbors  and  bays  of  all 
lands.  The  species  most  frequently  found  from  Massachusetts 
southward  is  Aure'lia  flavid'ula  (Fig.  134).  This  jellyfish 
reaches  the  diameter  of  fifteen  inches. 

In  various  details  of  structure  Aurelia  resembles  the 
medusa  of  certain  hydroids,  and  also  the  sea-anemones,  the 
coral  polyp,  and  the  fresh-water  polyp.  The  mouth  opens  at 
the  center  of  the  under  surface  into  a  large  cavity  which 
branches  freely  into  many  tubes  running  to  the  circumference, 
where  they  join  the  circular  canal.  Between  the  ectoderm 


268  GENERAL  ZOOLOGY 

covering  the  body,  and  the  endoderm  lining  the  gastrovascu- 
lar  cavity,  is  a  great  mass  of  jelly  secreted  by  the  cells  of  the 
two  layers.  Hanging  from  about  the  mouth  are  four  broad 
ribbon-like  appendages  called  u  lips."  These  and  the  delicate 
fringe  of  tentacles  at  the  rim  of  the  bell  are  covered  with 
nettle-cells.  Nettle-cells  are  found  also  on  the  mesenterial 
filaments  which  lie  in  the  radial  canals. 


FIG.  134.  Photograph  of  Jellyfish.    Reduced 

A  very  noticeable  detail  of  structure  that  one  observes  in 
watching  these  animals  in  the  water,  especially  in  the  late 
summer,  is  the  set  of  four  partial  rings  about  the  center, 
yellowish  in  color  in  the  males  and  reddish  in  the  females. 
These  rings  are  the  sexual  glands.  They  are  sacs  which  con- 
tain the  eggs  or  spermatozoa  until  these  cells  are  ready  to  be 
discharged  through  the  radial  canals  and  the  mouth.  On  the 
rim  of  the  bell,  at  eight  equidistant  points,  are  small,  rounded 


THE   SEA-ANEMONE  AND   SOME  ALLIES        269 

sense-organs,  which  have  the  function  of  controlling,  through 
the  nervous  and  muscular  systems,  the  direction  of  movement 
of  the  jellyfish.  The  most  important  muscle  is  a  circular 
band  near  the  rim.  The  nerve-cells  are  grouped  near  the 
sense-organs,  and  connect  the  latter  with  the  muscle-band. 
When  the  circular  muscle  contracts,  the  bell  becomes  more 
convex,  and  the  resulting  action  of  the  water  in  the  hollow 
of  the  bell  against  the  water  outside,  sends  the  animal  along 
in  a  slow,  periodic,  pulsating  movement. 

The  development  of  Aurelia  is  very  different  from  that  of 
the  hydro  ids.  The  simple,  free-swimming  larva  of  Aurelia 
sinks  to  the  bottom,  attaches  itself  to  some  fixed  object, 
and  takes  on  a  form  resembling  Hydra.  The  formation  of 
circular  grooves  below  the  tentacles  develops  a  series  of  saucer- 
like  divisions,  one  within  another.  These  separate  and,  swim- 
ming away  with  the  convex,  aboral  surface  uppermost,  grow 
into  the  adult  form.  The  fixed  stage  is  comparable  with  the 
hydroid  generation  of  Hydrozoa. 

Aurelia  is  but  slightly  more  dense  than  the  sea-water  itself. 
According  to  one  authority  there  is  less  than  one  eighth  of  one 
per  cent  of  proteid  material  present.  Thus  over  ninety-nine 
per  cent  is  water.  The  small  amount  of  proteid  material  in 
the  body  of  Aurelia  makes  it  very  unlikely  that  many  animals 
depend  on  them  for  food.  After  a  storm  in  summer  great 
numbers  of  Aurelise  may  be  found  on  the  shore.  In  a  few 
hours  only  scattered  films  are  left  on  the  sand  to  show  where 
the  animals  lay.  The  destruction  of  many  Aureliao  is  to  be 
expected  because  of  their  general  helplessness,  but  annihila- 
tion of  the  species  is  prevented  by  the  enormous  number  of 
young  produced. 

The  great  fecundity  of  Aurelia  and  its  giant  relative  Cya'nea 
which  sometimes  grows  to  a  diameter  of  eight  feet,  might 
threaten  to  fill  the  ocean  with  their  bodies,  were  it  not  for 
the  fact  that  neither  lives  over  the  winter.  The  young  start 


270 


GENERAL  ZOOLOGY 


their  development  in  the  autumn  and  complete  it  in  the 
spring.  It  is  a  self-evident  fact,  in  this  instance  at  least, 
that  death  is  a  benefit,  not  only  to  all  other  forms  of  sea  life, 
but  even  to  the  race  of  Aurelia  itself.  The  adults  swallow 
everything  that  can  be  taken  into  the  mouth,  but  probably 
their  most  abundant  food  is  small  pelagic  Crustacea  similar 
to  Cyclops  (Fig.  75). 

The  class  of  which  Aurelia  flavidula  is  a  representative  is 
called  Scyphozo'a  (Gr.  skyphos,  cup  ;  zoa,  animals). 


FIG.  135.  Photograph  of  Comb-Jelly.    Enlarged 

The  Comb-Jelly.  The  species  of  "comb-jelly,"  or  "sea- 
walnut,"  shown  in  Fig.  135  (Pleurobrach'ia  rlwdodac'tyla), 
is  found  in  the  colder  seasons  floating  at  the  surface  along 
the  North  Atlantic  coast.  It  is  about  as  large  as  a  hazelnut, 
but  greater  in  diameter  vertically  than  tranversely. 


THE  SEA-ANEMONE  AND   SOME  ALLIES        271 

The  body  of  the  comb-jelly  is  soft  like  that  of  the  jellyfish, 
but  the  plan  of  structure  and  the  organs  are  somewhat  differ- 
ent. There  are  eight  meridional  bands  of  comb-like  struc- 
tures, which  serve  the  animal  as  locomotor  organs.  During 
locomotion  these  combs  move  vigorously,  and  in  such  a  way 
that  beautiful  iridescent  effects  are  produced  by  them. 
Near  the  lower  end,  as  shown  in  the  figure,  there  are  two 
fringed  tentacles  with  such  wonderful  powers  of  extension 
that  from  a  mass  no  larger  than  a  pin-head  they  can  extend 
over  a  foot.  The  tentacles  have  minute  adhesive  cells  which 
are  thought  to  be  .modifications  of  nettling-capsules,  or  struc- 
tures which  take  the  place  of  them.  By  means  of  the  adhe- 
sive cells  the  tentacles  hold  small  animals  and  pass  them  to 
the  mouth.  As  the  animal  swims  the  tentacles  are  below 
and  the  mouth  above.  A  funnel-shaped  space  at  the  upper 
end  carries  the  food  into  the  mouth.  The  gastro vascular 
cavity  extends  into  two  lateral  pouches  from  which  two 
branches  arise,  making  four;  each  of  the  four  branch-tubes 
gives  rise  to  two,  making  eight  altogether.  Each  of  the  eight 
branch-tubes  joins  a  meridional  tube  which  lies  just  beneath 
the  bands  of  combs.  Food  carried  in  at  the  mouth  can  thus 
pass  to  any  portion  of  the  body.  At  the  end  opposite  the 
mouth  there  is  a  small  sense-organ,  which  is  the  center  of 
the  animal's  nervous  system.  Every  comb-jelly  contains  both 
egg-cells  and  sperm-cells.  The  eggs  are  fertilized  outside  the 
body,  and  the  young  larvae  swim  free  and  gradually  develop 
into  the  adult  form.  The  comb-jelly  produces  a  phosphor- 
escent light  when  disturbed. 

The  class  of  which  Pleurobrachia  rhododactyla  is  a  repre- 
sentative is  called  Ctenoph'ora  (Gr.  Jcteis  (Jcten),  comb;  phero, 
bear). 

Definition  of  Coelentera  (Gr.  koilos,  hollow  ;  enteros,  intes- 
tine). Arranged  in  the  order  of  their  increasing  degree  of 
specialization,  the  four  classes  that  make  up  the  phylum 


272  GENERAL  ZOOLOGY 

Coelen'tera  are  Hydrozoa,  Scyphozoa,  Actinozoa,  and  Cte- 
nophora.  The  classes  constitute  a  fairly  distinct  phylum  by 
including  animals  with  radially  symmetrical  bodies  (at  least 
in  external  appearance)  in  which  there  is  but  one  cavity. 
This  cavity,  joining  the  mouth-opening,  is  the  digestive 
cavity,  and  is  not  separated  from  a  body-cavity,  as  in  higher 
animals  (whence  the  derivation  of  the  name  of  the  phylum). 
The  body  develops  from  an  embryo  that  has  two  germ-layers, 
-  the  ectoderm  and  the  endoderm.  In  this  particular  it  is 
different  from  every  phylum  of  animals  heretofore  described. 
The  characteristic  organs  of  offense  and  defense  are  the  net- 
tling-capsules.  By  some  authorities  the  Ctenophora  are 
separated  into  a  phylum  by  themselves,  partly  because  they 
do  not  possess  nettling-capsules. 


THE  FRESH- WATER  SPONGE  AND  SOME  ALLIES :  PORIFERA 

The  unending  shapes  of  plants,  the  rainbow's  varied  hues, 
All  these,  the  lowly  sponge  on  ocean's  bed  renews. 

The  Fresh-Water  Sponge.  The  sponge  illustrated  in  Fig. 
136  (Heteromeye'nia  ry'deri)  is  found  quite  generally  in  ponds 
and  quiet  brooks,  at  least  as  far  west  as  the  Mississippi  River. 
It  grows  on  the  under  side  of  overhanging  submerged  rocks, 
and  on  dead  sticks  and  leaves.  The  largest  specimens  are 
not  usually  more  than  one  inch  across.  Each  mass  of  sponge 
clings  flat  against  the  supporting  substance,  and  seldom  is 
more  than  one  eighth  of  an  inch  thick.  The  sponge  yields 
slightly  on  being  pressed  with  the  finger.  The  surface  looks 
rough,  but  to  the  touch  it  is  smooth.  The  color  is  grayish; 
occasionally  specimens  are  found  with  a  part  or  all  of  the 
mass  green.  This  is  due  to  the  presence  of  a  green  alga 
growing  in  the  sponge. 

The  first  thing  that  attracts  one's  attention  in  the  drawings 
of  the  fresh-water  sponge  is  the  many  small,  circular  holes, 
oscula  (sing,  osculum,  a  little  mouth),  scattered  over  the  surface. 
They  are  openings  through  which  the  waste,  the  unused  food, 
and  water  are  expelled  from  the  sponge.  Everywhere  between 
the  oscula  are  numerous  very  small  holes,  dermal  pores  (com- 
pare Fig.  137,  5),  which  open  into  quite  large  subdermal  cham- 
bers. Leading  from  the  subdermal  chambers  are  short  canals 
called  incur  rent  canals.  These  lead  to  cavities  lying  deeper 
in  the  sponge,  the  ampullce  (Fig.  137,  c),  which  are  lined 
with  cells  that  bear  flagella  (lashes).  These  cells  are  called 
collar-cells,  on  account  of  their  having  a  collar-like  membrane 

273 


274 


GENERAL  ZOOLOGY 


around  the  base  of  the  flagellum.  The  flagella  wave  inward 
and  cause  a  current  of  water  to  flow  into  the  sponge  through 
the  minute  dermal  pores  and  along  the  incurrent  canals, 
past  the  collar-cells  into  the  excurrent  canals.  Water  passes 


FIG.  136.  Fresh-Water  Sponge.  Upper 
portion  of  figure  natural  size;  lower 
portion  enlarged 

from  the  excurrent  canals 
into  the  cloaca,  —  a  large 
chamber  just  below  the  os- 
culum,  —  and  thence  flows 
out  of  the  sponge  through  the  osculum  (Fig.  137,  d). 

Food  consisting  of  microscopic  plants  and  animals  is  drawn 
in  at  the  dermal  pores  and  carried  along  by  the  current. 
Very  small  particles  are  taken  into  certain  cells  along  the 
canals  and  digested  there,  as  in  the  endodermal  cells  of  Hydra. 
Larger  particles  are  surrounded  by  ivandering  cells  and 
digested  little  by  little.  Digested  food  passes  by  osmosis  to 
all  the  cells  of  the  sponge. 


FRESH-WATER  SPONGE  AND  SOME  ALLIES     275 


The  fresh-water  sponge  has  no  special  digestive  organs, 
no  circulatory  system,  respiratory  system,  muscular  system, 
nervous  system,  nor  sense-organs.  Food  and  oxygen  are 
carried  in  together,  and  oxidation  takes  place  freely  because 
oxygen  can  go  anywhere  within  the  sponge.  The  oscula 
sometimes  contract  when  the  sponge  is  disturbed,  but  this 
action  takes  place  because  of  the  power  of  contracting  which 
is  possessed  by  certain  cells  that  are  not  true  muscle-cells. 
There  are,  however,  two  important  systems  of  organs  pos- 
sessed by  the  fresh- 
water sponge:  a  set 
of  structures  which 
constitute  the  skele- 
ton, and  special 
cells  for  reproduc- 
tion. The  substance 

'V  1NX^^«^^yJ^^ 

which    serves    as    a  ^    --c 

skeleton  supporting  FIG.  137.  Section  of  Fresh- Water  Sponge  (Spon- 
the  soft,  protoplas- 
mic cells,  is  made 
up  of  microscopic 
spicules  (compare  Fig.  139)  of  various  forms,  and  of  very  hard 
material  called  silica.  These  spicules,  interlacing  a-nd  cross- 
ing one  another,  give  a  very  firm  texture  to  organisms  that 
would  otherwise  be  formless  and  slimy. 

Certain  cells  along  the  canals  develop  eggs  and  sperma- 
tozoa. Each  sponge-mass  is  capable  of  producing  both  kinds 
of  cells,  but  not  at  the  same  time.  While  some  masses  are 
producing  eggs,  others  in  the  same  pond  or  brook  are  pro- 
ducing spermatozoa.  The  eggs  are  retained  in  position  on  the 
canals,  while  from  other  specimens  the  spermatozoa  escape  and 
swim  out  into  the  water,  to  be  drawn  later,  quite  by  accident, 
into  the  incurrent  canals  of  sponges  with  eggs.  The  eggs  are 
fertilized  and  immediately  begin  the  process  of  development. 


a,  surface; 


Much  enlarged     (After  Huxley) 

,  dermal  pores ;  c,  ampullae,  lined  with 
collar-cells ;  d,  osculum 


276 


GENERAL  ZOOLOGY 


When  the  embryo  has  reached  the  blastula  stage  it  is  set  free, 
and  swims  out  through  the  osculum.  The  larva,  in  SpongiVla, 
another  fresh-water  sponge,  and  probably  in  Heteromeyenia 
as  well,  is  shaped  like  a  hen's  egg,  but  is  very  small  and  is 
covered  with  collar-cells  bearing  flagella,  which  are  the  organs 
of  locomotion  for  the  few  hours  of  free  life  Avhich  the  larva 
has.  When  it  comes  to  rest  it  attaches  itself  by  the  broad 
end,  and  grows  into  the  form  of  the  adult. 

Fresh-water  sponges  reproduce  also  by  means  of  special 
organs  called  gemmules,  which  are  about  one-fiftieth  of  an  inch 
in  diameter  (Figs.  136  and  138).  These  structures  are  pro- 
duced in  the  sponge-mass  toward  the  end  of  August.  Their 
use  is  to  carry  the  species  over  the  unfavorable  season  after  the 
destruction  of  the  parent  sponge,  which  usually  takes  place  in 
the  fall.  They  are  admirably  protected  by  the  three  layers  of 
material  which  form  the  horny  covering.  The  double-headed 
spicules  give  stiffness  to  the  whole  gemmule.  Inside  is  a  mass 

of  cells  containing  food-material; 
these  cells  remain  in  a  state  of 
inactivity  until  the  return  of 
favorable  conditions.  Then  the 
contents  of  the  gemmule  forces 
itself  through  the  thinly  covered 
pore,  and  soon  forms  a  minute 
sponge  with  incurrent  canals 
and  a  single  osculum,  which,  as 
Professor  Potts  says,  "  puffs  out 
material  after  the  manner  of  a 
miniature  volcano." 
By  far  the  greater  number  of  species  of  marine  sponges, 
and  all  fresh-water  sponges,  are  composite  in  character.  In 
hydroids  it  is  easy  to  distinguish  one  individual  of  a  colony 
from  another,  but  in  fresh-water  sponges  the  only  clew  one 
can  get  to  the  number  of  individuals  is  that  furnished  by  the 


FIG.  138.  Gemmule  of  Fresh- 
Water  Sponge.  Much  enlarged. 
(After  Evans) 


FRESH-WATER  SPONGE  AND  SOME  ALLIES     277 


number  of  oscula.  The  evidence  obtained  through  studying 
the  embryology  of  sponges  indicates  that  each  osculum  marks 
the  position  of  an  individual,  and  that  the  adult  form  results 
from  the  fusion  of  numerous  individuals  originally  distinct. 
Internally,  however,  there  is  no  sepa- 
ration between  individuals,  their 
chambers  being  continuous. 

Sycon.  Some  sponges  that  live  in 
the  sea  are  simple ;  that  is,  they  con- 
sist of  a  single  individual.  A  sponge 
of  this  kind  is  Sy'con  (Fig.  139).  The 
free  end  has  a  single  osculum.  All 
over  the  body  elsewhere  are  minute 
dermal  pores  leading  into  in  current 
canals,  alternating  in  the  substance 
of  the  body-wall  with  radial  canals. 
Food  and  water  entering  the  incur- 
rent  canals  by  dermal  pores  are 
carried  into  the  adjacent  radial  canals 
by  short  canals.  From  the  radial 
canals  the  water  passes  into  the  large 
cloaca.  Waste  and  extra  water  are 
discharged  through  the  osculum.  The  spicules  are  composed 
of  carbonate  of  lime. 

The  Bath-Sponge.  The  best  known  of  all  species  of  sponges 
is,  of  course,  the  bath-sponge  (Euspon'gia  officina'lis).  It  is  a 
composite  sponge  of  great  complexity,  but  usually  the  oscula, 
looking  like  chimneys,  stand  out  so  clearly  that  one  may  deter- 
mine the  number  of  individuals  present  in  a  mass.  Varieties  of 
this  sponge  are  found  in  the  deep  waters  about  the  Bahama 
Islands  and  in  the  Mediterranean  Sea,  especially  on  the  coast 
of  the  Turkish  dominions. 

The  bath-sponge  grows  attached  to  rocks  in  water  of  a  few 
fathoms'  depth.  Divers  cut  the  masses  at  the  base  and  later 


FIG.  139.  Sycon  and  Spic- 
ules. Sponge  enlarged; 
spicules  much  enlarged. 
(After  Grentzenberg) 


278  GENERAL  ZOOLOGY 

throw  them  upon  the  beach,  where  the  soft  portion  rots  and 
dries.  Then  the  remainder,  which  is  the  skeleton,  is  cleaned 
and  made  ready  for  the  market.  These  sponges  are  valuable 
for  the  uses  of  man  on  account  of  the  softness  of  the  whole 
skeleton  and  the  tenacity  of  its  substance.  The  skeleton  is 
composed  of  tough,  anastomosing  fibers  of  horny  material 
instead  of  spicules  of  silica,  as  in  Heteromeyenia,  or  of  car- 
bonate of  lime,  as  in  Sycon. 

Relation  to  Environment.  Perhaps  no  group  of  animals  has 
so  wide  a  distribution  in  water  as  sponges.  In  fresh  water, 
and  in  the  sea  from  the  very  margin  of  low  tide  to  the  greatest 
depth  of  ocean  yet  explored,  and  in  all  zones,  various  species 
of  sponges  are  found.  They  live  in  every  conceivable  situa- 
tion, adapting  themselves  in  form  of  mass  to  the  particular 
place  in  which  they  grow.  Branched  species,  like  Microci'ona 
prolifera^  in  the  frontispiece,  vary  much  in  form  and  arrange- 
ment of  branch.  Incrusting  species  on  rocks,  as  in  the  fron- 
tispiece, and  as  shown  growing  about  barnacles,  Fig.  77, 
follow  every  turn  of  the  supporting  substance.  One  species 
of  Clio'na  grows  on  shells  of  mollusks,  and  through  the 
agency  of  a  secretion  of  its  protoplasm  consumes  the  sub- 
stance of  the  shell  and  grows  to  fill  the  space  thus  made. 
In  regions  where  the  ocean-bottom  is  muddy,  sponges  grow 
stalks  that  keep  the  mass  away  from  the  mud,  which  if 
stirred  up  would  smother  the  colony. 

Many  marine  sponges  being  thick  and  massive,  and  of  loose 
texture,  like  the  sulphur  sponges,  are  very  convenient  har- 
bors of  refuge  for  myriads  of  small  animals,  chiefly  Crustacea 
and  worms.  Undoubtedly  the  odor  of  living  sponges,  described 
by  one  investigator  as  resembling  garlic,  drives  away  fishes 
and  other  ravenous  animals  of  large  size  that  might  feed  on 
the  little  guests,  or  even  on  the  sponge  itself. 

Definition  of  Porifera  (Lat.  porns,  pore ;  ferre,  to  bear). 
By  most  investigators  the  sponges  are  considered  a  distinct 


FRESH-WATER  SPONGE  AND  SOME  ALLIES     279 

phylum  Porif'era,  including  only  a  single  class.  It  is  evident 
that  the  Porifera  are  lower  in  organization  than  the  Ccelen- 
tera,  for  the  members  of  the  phylum  do  not  show  indications 
of  muscle-cells,  of  nerve-cells,  or  of  sense-organs.  Neither  are 
there  special  organs  of  offense.  Protection  is  afforded  by  the 
spicules  and  the  characteristic  odor.  Sponges  are  the  lowest 
animals  which  reproduce  by  eggs  and  spermatozoa.  In  devel- 
opment two  germ-layers  are  present,  ectoderm  and  endoderm, 
and  a  middle  undifferentiated  layer  called  the  mesoglwa. 


CHAPTER   XXI 
AMOEBA  AND  SOME  ALLIES:  PROTOZOA 

Gradual,  from  these  what  numerous  kinds  descend, 
Evading  even  the  microscopic  eye  ! 
Full  nature  swarms  with  life,  —  one  wondrous  mass 
Of  animals,  or  atoms  organized. 

JAMES  THOMSON,  Summer. 

Amoeba.  The  amoeba  (Amce'ba  pro' tens,  Fig.  140)  is  com- 
mon in  stagnant  water  of  all  lands,  but  it  is  so  minute 
that  it  is  impossible  to  be  sure  of  its  presence  in  a  given 
place  until  examination  has  been  made  with  a  compound 
microscope. 

One  of  the  best  ways  to  find  large  specimens  of  the 
amoeba  is  to  remove  carefully  from  the  bottom  of  a  well- 
stocked  fresh-water  aquarium  a  few  dead  leaves.  A  medi- 
cine-dropper full  of  material  from  the  surface  of  one  of  the 
leaves  may  yield  several  specimens.  A  short  time  after  a  few 
drops  of  the  water  have  been  mounted  on  a  glass  slide  the 
Amoebae  will  exhibit  the  characteristic  structure  and  activities. 
The  usual  diameter  of  an  amoeba  is  about  .5  mm.  (^  inch). 

The  beginner  in  microscopy  is  very  likely  to  overlook  an 
amoeba  altogether,  or  to  think  in  his  anxiety  that  every  little 
irregular  clear  spot  in  the  field  of  his  microscope-objective 
is  one.  The  active  amoeba  is  never  the  same  in  appearance  in 
consecutive  moments.  The  outline,  at  all  times  irregular  in 
locomotion,  constantly  becomes  more  or  less  so,  by  the  increase 
or  decrease  in  prominence  of  little  processes  called  pseudo- 
podia  (false  feet),  which  extend  in  one  or  several  directions. 

Amoeba  is  a  complete  organism,  although  it  is  composed  of 
a  single  cell.  The  substance  of  the  cell  is  protoplasm,  — that 


AMCEBA  AND   SOME  ALLIES:    PROTOZOA       281 

complicated  substance  without  which  life  cannot  exist.  The 
principal  organ  of  the  cell  is  the  nucleus,  composed  of  pro- 
toplasm more  dense  than  that  which  surrounds  the  nucleus. 
Frequently  zoologists  distinguish  the  protoplasm  of  the 
nucleus,  nudeoplasm,  from  that  of  the  cell-body  or  cytoplasm. 
The  nucleus  is  usually  quite  difficult  to  see  unless  the  amoeba 
is  killed  by  chemicals  and 

its  protoplasm  "fixed"  and  ^-,. ^§|fcj 

stained.     The   cytoplasm  is  ^:9j^^^ 

finely  granular  all  through,  VSIflfli 

except   for  a  thin  layer  on        lii|Sfe:>....--;:"-'-N  I.SSR! 

the  surface,  which  is  always    /^ip-fSSSS^F'S-v;-;:? 4lS*l-/ 

clear  and  without  granules.    Sk^^~:£^^SS^S?Q' 

The    granular   part    of    the  ^^S^ 

cytoplasm   is   called   endo- 

plasm,  and  the  non-granular 

sheath  the  ectoplasm.  FlG- 14(X  Amceba'   Much  enlar£ed 

During    locomotion    the      <From  Sedgwick  and  Wilson's  General 
°.  „      ,    ,  Biology) 

pseudopodia  are  first  formed 

of  the  ectoplasm,  the  endoplasm  following  immediately  and 
continually  in  the  same  direction  that  the  ectoplasm  takes. 
The  method  of  locomotion  in  Amoeba,  as  stated  by  Professor 
H.  S.  Jennings,  of  the  University  of  Pennsylvania,  is  as 
follows.  "  Locomotion  in  Amoeba  is  a  process  that  may  be 
compared  with  rolling,  the  upper  and  lower  surfaces  contin- 
ually interchanging  positions.  » This  is  shown  by  observation 
of  the  movements  of  particles  attached  to  the  outer  surface 
or  imbedded  in  the  ectosarc  [ectoplasm]  of  the  animal.  Such 
attached  particles  move  forward  on  the  upper  surface  and 
over  the  anterior  edge,  remain  quiet  on  the  under  surface 
till  the  body  of  the  amoeba  has  passed,  then  pass  upward  at 
the  posterior  end,  and  forward  on  the  upper  surface  again. 
Single  particles  may  thus  be  observed  to  make  many  com- 
plete revolutions." 


282  GENERAL  ZOOLOGY 

When  the  advancing  pseudopodia  come  in  contact  with  a 
minute  unicellular  organism,  the  object  may  be  enveloped;  if 
so,  it  gradually  sinks  into  the  cytoplasm,  the  amoeba  mean- 
time continuing  its  rolling  locomotion;  if  the  object  is  useless 
for  food,  the  amoeba  simply  rolls  over  it,  leaving  it  behind. 
Food  is  taken  in  with  a  small  amount  of  water  which  forms 
a  surrounding  bubble  or  vacuole.  This  food-vacuole  is  carried 
about  in  the  endoplasm  and  slowly  disappears  in  the  process 
of  digestion,  which  goes  on  quite  as  effectively  in  the  amoeba 
as  in  any  of  the  higher  animals.  The  indigestible  particles  of 
the  food  are  left  behind  as  the  amoeba  rolls  along. 

All  the  other  phases  of  metabolism  go  on  as  in  many-cell 
animals,  except  that  in  the  amoeba  everything  must  be  done 
in  the  one  cell.  The  oxygen  which  the  animal  needs  probably 
comes  in  through  the  general  surface  of  the  ectoplasm  by 
osmosis.  Oxidation  and  the  release  of  energy  take  place,  as 
is  manifested  in  locomotion.  The  waste  of  the  body  is  prob- 
ably partly  expelled  by  the  contractile  vacuole.  This  organ 
may  be  observed  in  that  portion  of  the  ectoplasm  which  is 
behind  in  locomotion.  The  products  of  metabolism  when 
brought  into  that  region  form  a  sphere  of  liquid  which,  as 
it  increases  in  size,  is  carried  back  from  the  region  of  the 
nucleus  to  the  point  where  it  contracts  and  bursts  on  the 
surface. 

Reproduction  in  Amoeba  is  accomplished  by  the  nucleus 
and  the  protoplasm  dividing  into  equal  portions,  the  two  new 
cells  separating  immediately  and  growing  to  the  size  of  the 
original  one.  This  kind  of  reproduction  is  considered  by 
many  zoologists  to  be  a  phase  of  growth.  The  cell,  by  feed- 
ing, becomes  so  large  that  the  surface  through  which  food  and 
oxygen  pass  is  not  great  enough  to  supply  the  more  rapidly 
increasing  volume  of  cytoplasm.  When  division  takes  place, 
masses  are  produced  which  have  enough  surface  to  supply  the 
interior  with  material  for  growth  and  other  forms  of  energy. 


AMCEBA  AND  SOME  ALLIES:    PROTOZOA       283 

Under  certain  conditions  of  the  environment  the  amoeba 
ceases  moving  about;  it  takes  on  the  form  of  a  ball,  and 
incloses  itself  in  a  membrane  or  cyst.  The  encysted  amoeba 
remains  in  that  state  until  the  return  of  favorable  conditions 
in  its  habitat. 

Euglena.  A  relative  of  Amoeba,  found  in  the  same  situ- 
ations, is  Eugle'na  vir'idis  (Fig.  141) ;  it  also  is  composed  of 
one  cell.  Euglena  has  a  more  fixed  arrangement  of  parts 
than  Amoeba.  There  is  a  blunt  anterior  end  with  a  short, 
funnel-shaped  mouth  to  carry  food  into  the  cytoplasm.  Out 
of  the  mouth  extends  a  long  lash,  which  by  its  whip-like 
vibrations  carries  the  animal  through  the  water,  and  at 
the  same  time  sends  food  back  to  the  mouth.  Behind  the 
mouth  is  a  small  red  eye-spot,  which  lies  beside  a  clear 
space.  This  clear  space  has  been  found  to  be  sensitive  to 
light.  The  nucleus  is  near  the  middle  of  the  body,  and 
can  be  seen  easily  in  the  living  animal,  although 
the  cytoplasm  immediately  about  it  is  colored 
quite  green  with 
chlorophyll,  —  a 
coloring  matter 
found  in  the 

green  parts  of  FlG  141  Euglena.  Much  enlarged.  (After  Saville  Kent) 
plants. 

Many  biologists  believe  that  Euglena  is  indeed  a  plant 
because,  through  the  agency  of  its  chlorophyll,  it  can  use  car- 
bon dioxide  as  a  raw  food-material,  retaining  the  carbon  and 
giving  off  oxygen  when  the  organism  is  in  the  light.  This 
creature  illustrates  the  fact  that  it  is  impossible  to  classify 
all  organisms  as  plants  or  animals. 

As  a  rule  Euglena  moves  with  the  lash  forward,  but  the 
animal  can  turn  in  any  direction,  and  can  even  change 
the  shape  of  its  body  considerably,  but  it  does  not  form 
pseudopodia.  Sometimes  when  being  experimented  011  with 


284  GENERAL  ZOOLOGY 

substances  which  it  does  not  like,  Euglena  ceases  moving, 
contracts  into  a  ball,  and  encysts  itself,  just  as  it  does  in 
nature  when  it  is  surrounded  by  unfavorable  conditions. 

The  Malarial  Parasite.  Many  one-cell  animals  are  parasitic. 
One  of  the  most  studied  in  recent  years  is  the  malarial  para- 
site of  man  (Plasmo'dium  mala' rice,  Fig.  142).  The  life-history 
of  this  organism  is  long  and  complicated,  but  we  can  get  a  fair 
understanding  of  its  principal  phases  without  discussing  the 
minutest  details. 

In  its  simplest  form  the  animal  resembles  an  extremely 
small  amoeba.  In  that  stage  it  is  found  in  the  red  corpuscles 
of  human  blood.  There  the  parasite  increases  in  size  until  it 
almost  fills  the  corpuscle  (Fig.  142,  4) ;  then  it  divides  into 
small  bodies  called  spores  (Fig.  142,  5av).  The  process  of 
spore-formation  causes  the  chill  that  accompanies  malaria. 
When  the  spores  burst  from  their  spore-case  (Fig.  142,  5aVI) 
and  from  the  blood-corpuscles,  a  quantity  of  poisonous  mate- 
rial (represented  by  black  dots  in  Fig.  142,  5«YI)  is  released 
and  mingles  with  the  liquid  of  the  blood.  This  poisonous 
material  induces  the  fever  which  always  follows  the  chill. 
The  released  spores  may  enter  red  corpuscles  again,  and  in 
forty-eight  hours  in  one  type  of  malaria,  and  seventy-two 
hours  in  another,  form  spores  once  more. 

Some  of  the  amoebulce  (amoeba-like  stages)  of  the  parasite 
have  a  different  history.  While  most  of  them  in  the  red  cor- 
puscles of  a  person  go  on  reproducing  non-sexually,  as  just 
described,  some  develop  into  a  form  which,  by  comparison 
with  higher  animals,  we  call  the  female  cell  (Fig.  142,  5cn), 
and  others  into  male  cells  (Fig.  142,  5Z>n*).  If  now  the  person 
be  exposed  to  the  bite  of  a  mosquito  of  the  genus  Anopheles 
(see  p.  63),  the  male  and  female  cells  of  Plasmodium  each 
reach  their  full  development  in  the  human  red  blood-corpus- 
cles, as  these  rest  in  the  stomach  of  the  mosquito.  Leaving 
the  corpuscles,  the  two  cells  unite  to  form  a  worm-like  cell 


11 


13 


SCHEMA 


FIG.  142.    Life-Cycle  of  Malarial  Parasite.    (After  Grassi) 


285 


286  GENERAL  ZOOLOGY 

(Fig.  142,  6),  which  penetrates  to  the  outer  wall  of  the  stomach 
of  the  mosquito,  where  it  increases  in  size  to  form  a  large 
sphere  (Fig.  142, 12).  In  a  short  time  the  sphere  subdivides 
into  countless  extremely  minute  blasts  (Fig.  142, 17,  l).  These 
make  their  way  through  the  body-cavity  of  the  mosquito  to 
the  salivary  glands.  Penetrating  to  the  interior  of  those 
glands,  the  blasts  enter  the  ducts,  and  are  carried  outward 
and  down  the  insect's  proboscis  by  the  saliva  when  the 
mosquito  bites  another  person.  Then  in  the  human  blood 
the  blasts  enter  the  red  corpuscles  and  become  amcebulce, 
thus  completing  a  cycle. 

Prominent  among  the  scientific  men  who  since  1896  have 
discovered  the  facts  of  the  life-history  of  the  malarial  para- 
site are  Dr.  Ross,  of  India,  and  Professor  Grassi,  of  Italy. 
Upon  their  discoveries,  and  those  of  others,  are  based  the 
numerous  operations  against  the  mosquito  in  the  vicinity  of 
large  cities. 

Paramoecium.  Perhaps  no  member  of  the  phylum  under 
discussion  in  this  chapter  has  been  observed  by  more 
students  than  has  the  slipper-animalcule,  Paramce'cium  cau- 
da'tum  (Fig.  143  A,  B) ;  and  no  member  of  its  phylum  has 
been  so  frequently  made  the  basis  of  scientific  discussions  of 
cell-structure  and  cell-physiology.  Paramoecium  lives  in  stag- 
nant pools  of  fresh  water  in  all  lands.  Specimens  may  be 
obtained  in  countless  numbers  by  placing  a  quantity  of  hay 
in  a  jar  of  ordinary  water  and  leaving  it  to  stand  for  a  few 
weeks.  The  bacteria  developed  in  the  decaying  hay  furnish 
an  inexhaustible  food-supply  for  the  animals. 

As  in  Amoeba,  Euglena,  and  Plasmodium,  the  entire  body 
of  Paramoecium  is  a  single  cell.  The  cell  when  moving 
freely  has  a  definite  shape,  although  it  changes  constantly  in 
outline,  owing  to  the  fact  that  the  irregularities  in  the  body 
are  whirled  into  view  as  the  animal  swims  along  in  a  slender 
spiral  path. 


AMCEBA  AND  SOME  ALLIES:    PROTOZOA       287 


Paramoecium  is  about  .2  mm.  (^  inch)  in  length.  T<he 
anterior  end  is  rounded  and  the  posterior  end  pointed. 
Right  and  left  sides  are,  as  indicated  in  the  figures,  deter- 
mined by  the  position  of  the  mouth  (Fig.  143,  2),  which  is 
on  a  surface  called  ventral. 
The  entire  surface  of  the 
ectoplasm  is  covered  with 
great  numbers  of  short, 
hair-like  structures,  called 
cilia  (Fig.  143,  l).  The  cilia 
are  the  organs  of  locomo- 
tion. Their  customary 
manner  of  working  is  to 
wave  backward  toward  the 
posterior  end,  propelling 
the  animal  forward,  but 
they  may  also  wave  so  as  6-:-. 
to  send  the  body  along 
with  the  pointed  end  for- 
ward. A  few  cilia  j5pm£- 
what  longer  than  the 
Others  lie  in  the  groove  FIG.  143.  Paramoecium.  Much  enlarged 
that  leads  diagonally  across 
the  ventral  surface  to  the 
mouth.  Their  function  *is 


B 


A,  left  side;  B,  ventral  surface;  1,  cilia; 
2,  mouth;  3,  gullet;  4,  food-vacuole 
forming;  5,  food-vacuole  in  cytoplasm; 
6,  anus;  7,  contractile  vacuole ;  8,  mac- 
ronucleus ;  9,  micronucleus 

(From  Sedgwick  and  Wilson's  General 
Biology) 


to  carry  the  food  down  the 
short  gullet  into  the  endo- 
plasm. 

The  endoplasm,  which,  as  already  explained,  is  that  por- 
tion of  the  cytoplasm  lying  between  the  nucleus  and  the  out- 
side layer  of  ectoplasm,  is  soft  and  semifluid.  Food  is  passed 
into  it  by  the  gullet  (Fig.  143,  3),  and  immediately  begins  to 
float  away  from  that  point,  surrounded  by  a  little  drop  of 
water.  These  masses  are  called  food-vacuoles  (Fig.  143,  4,  5). 


288 


GENERAL  ZOOLOGY 


While  the  current  in  the  cell-protoplasm  is  carrying  the  food- 
vacuoles  around,  digestive  fluid  formed  by  the  protoplasm 
is  breaking  up  the  food,  liquefying,  and  changing  it  chem- 
ically for  the  process  of  assimilation  or  building  up  into  pro- 
toplasm. The  indigestible  particles  are  discharged  from  the 
cell  by  a  small  opening,  the  anus  (Fig.  143,  6).  The  waste 
derived  from  the  food  and  protoplasm  that  is  used  up  in  the 
work  of  the  animal  is  probably  discharged  in  the  form  of 
liquid  from  two  special  organs,  one 
near  either  end  at  the  dorsal  surface. 
These  are  contractile  vacuoles  (Fig. 
143,  7).  It  is  supposed  that  the  liquid 
waste  when  formed,  flows  through  the 
protoplasm  along  somewhat  definite 
channels,  to  the  point  where  it  collects 
in  a  gradually  increasing  vacuole. 
Soon  the  maximum  size  is  attained, 
and  the  vacuole  bursts  at  the  surface, 
the  waste  pouring  into  the  water  out- 
side. The  two  contractile  vacuoles 
alternate  in  contracting. 

Paramcecium  has  two  nuclei ;  the 
large  one  is  called  the  macrvnucleus 
(Fig.  143,  8),  and  the  small  one  the 
micro  nucleus  (Fig.  143,  9).  The  macro- 
nucleus  is  thought  to  be  the  seat  of 
the  general  activities  of  the  cell,  while 
the  micronucleus  is  the  seat  of  the 
important  process  of  reproduction. 

The  theory  that  reproduction  by  divi- 
sion is  a  phase  of  growth  was  stated  in 

the  description  of  Amoeba.  Paramoecium  also  divides  into 
two  equivalent  cells  (Fig.  144),  with  half  the  macronucleus 
and  half  the  micronucleus  in  each,  probably  because  the 


FIG.  144.  Paramoecium 
dividing.  Much  en- 
larged 

1,  mouth  and  gullet; 
2,  macronucleus  divid- 
ing; 3,  micronucleus 
dividing 

(From  Sedgwick  and  Wil- 
son's General  Biology) 


AMCEBA  AND  SOME  ALLIES:    PROTOZOA       289 


volume  of  the  cell  becomes  too  great  to  be  kept  alive  by  the 
organs  of  the  relatively  decreasing  surface.  As  many  as 
three  or  four  generations  of  Paramoe- 
cia  may  be  produced  in  a  single  day. 
The  frequency  of  division  of  the  cell 
depends  upon  the  kind  and  abun- 
dance of  food  obtainable,  and  also  upon 
a  process  known  as  conjugation  (Fig. 
145).  This  complicated  process  was 
worked  out  in  great  detail  in  1888  by 
Maupas,  a  French  librarian,  who  in  his 
spare  time  studied  the  life-history  of 
Paramoecium  and  other  unicellular 
organisms. 

In  conjugation  two  Paramoecia  unite 
temporarily  in  the  manner  indicated  in 
the  figure.  A  fraction  of  the  micro- 
nucleus  of  each  passes  through  the 
two  contiguous  layers  of  ectoplasm 
and  unites  with  a  similar  fraction  in 
the  other  animal.  When  this  and  cer- 
tain other  less  essential  phenomena 
have  taken  place,  the  individuals  sep- 
arate and  continue  the  process  of  transverse  division,  but 
with  greater  frequency  than  before.  Maupas  interpreted 
conjugation  as  a  process  of  rejuvenescence,  or  renewing  the 
youth,  through  which  these  organisms,  being  exhausted  by  a 
long  series  of  divisions,  could  regain  their  vitality,  thus  pre- 
venting the  extermination  of  the  race.  It  has  been  pointed 
out  by  some  zoologists  that  conjugation  in  unicellular  organ- 
isms has  many  points  of  resemblance  with  the  union  of  egg 
and  spermatozoon  in  the  higher  animals.  We  may  therefore 
speak  of  conjugation  as  sexual  reproduction,  to  distinguish  it 
from  the  non-sexual  reproduction  by  division. 


FIG.  145.  Paramoecia  con- 
jugating.  Much  en- 
larged. (After  Saville 
Kent) 


290  GENERAL  ZOOLOGY 

Some  interesting  experiments  bearing  on  the  problem  of 
conjugation  in  Paramoecium  were  carried  out  in  the  years 
1901  and  1902  by  Professor  G.  N.  Calkins,  of  Columbia 
University.  He  found  that  as  the  generations  approached 
ninety  to  one  hundred  and  seventy  in  number,  the  individuals 
become  smaller  in  size  and  appear  to  lose  some  property  in 
their  protoplasm.  He  was  able  to  "  renew  the  youth  "  of  his 
series  of  animals  by  artificial  means,  —  twice  by  change  of 
food,  once  by  mechanical  agitation,  and  once  by  a  rise  in 
temperature.  After  each  stimulation  the  Paramcecia  divided 
frequently,  and  in  other  respects  imitated  the  phenomena 
subsequent  to  conjugation. 

Results  strikingly  similar  to  these  have  been  obtained  by 
Professor  Jacques  Loeb,  of  the  University  of  California,  in 
stimulating  by  mechanical  and  chemical  means  the  eggs  of 
sea-urchins  to  develop  to  advanced  stages.  The  term  "  artifi- 
cial parthenogenesis  "  (see  parthenogenesis,  p.  34)  has  been 
used  in  describing  the  results  obtained  by  Professor  Loeb. 
It  is  interesting  to  notice  in  connection  with  these  experiments 
that  in  the  eggs  of  sea-urchins  stimulated  to  develop  naturally 
by  the  spermatozoon,  and  artificially  by  mechanical  and  chem- 
ical means,  and  in  Paramcecium  stimulated  to  frequent  divi- 
sion naturally  by  conjugation,  and  artificially  by  mechanical 
and  chemical  means,  we  have  a  result  the  identity  of  which 
can  be  expressed  under  the  name  rejuvenescence.  Although 
these  experiments  have  value  in  interpreting  the  phenomena 
of  reproduction,  it  is  well  to  keep  in  mind  the  fact  that  the 
artificial  method  fails  after  a  few  cycles  in  Paramoecium,  and 
before  the  end  of  the  larval  period  in  the  sea-urchin. 

When  the  water  in  which  Paramoecia  live  shows  indica- 
tions of  drying  up,  the  animals  encyst  themselves  by  secret- 
ing a  film  of  gelatinous  substance  from  their  ectoplasm.  The 
encysted  animal  retains  its  usual  form,  and  remains  inactive 
until  it  is  brought  into  water  again. 


AMCEBA  AND  SOME  ALLIES:    PROTOZOA       291 

Unicellular  organisms  have  long  been  objects  of  profound 
study  for  biologists  and  psychologists.  The  biologists  recog- 
nize in  them  the  morphological  unit  of  structure,  identical  in 
important  details  with  the  unit  of  structure  in  the  tissues  of 
all  animals  as  well  as  all  plants,  but  differing  from  the  tissue- 
cells  in  the  fact  that  the  latter  have  only  one  chief  function 
to  perform,  whereas  unicellular  organisms  carry  out  all  the 
processes  of  living  in  one  small  bit  of  protoplasm, — the  single 
cell.  Psychologists  look  to  these  organisms  for  the  beginning 
of  that  phase  of  mind  called  consciousness,  one  evidence  of 
which  we  see  in  the  ability  of  ourselves  and  other  animals  to 
choose  a  course  of  action.  As  a  matter  of  fact,  we  have  no 
way  of  knowing  whether  unicellular  organisms  are  conscious 
or  not.  According  to  Professor  Jennings,  these  organisms, 
as  well  as  others,  manifest  complicated  internal  physiological 
processes.  Any  external  agents,  as,  for  example,  oxygen,  heat, 
or  food,  which  bear  relation  to  the  internal  physiological 
processes,  are  concerned  in  the  activities  of  the  organism.  If 
a  Paramoecium  comes  to  a  place  where  oxygen  is  scarce,  it 
will  make  a  series  of  trial  trips  in  various  directions,  until  the 
internal  demand  for  oxygen  is  satisfied.  As  the  result  of 
the  needs  of  the  organism,  it  is  constantly  on  the  move,  but 
we  cannot  say  that  these  movements  are  conscious  efforts. 

Definition  of  Protozoa  (Gr.  protos,  first ;  zoon,  animal). 
The  four  members  of  the  phylum  described  in  this  chapter 
were  selected  as  representatives  of  the  four  classes  that  make 
up  the  phylum :  Amoeba  proteus,  of  the  class  Sarcodi'na ; 
Euglena  viridis,  class  MastigopJi' ora  ;  Plasmodium  malarise, 
class  Sporozo'a;  and  Paramoecium  caudatum,  class  Infuso'ria. 

Although  in  each  class  the  genera  differ  widely,  all  the 
members  of  the  four  classes  agree  in  being  composed  of 
single  cells.  Nearly  all  species  are  microscopic  in  size. 

Reproduction  is  brought  about  by  division  of  the  cell,  and 
never  by  eggs  and  spermatozoa. 


CHAPTER    XXII 

THE  EVOLUTION  OF  INVERTEBRATES  AND  THE  ANCESTRY 
OF  THE  VERTEBRATES 

I  wrote  the  past  in  characters 
Of  rock  and  fire  the  scroll, 
The  building  in  the  coral  sea, 
The  planting  of  the  coal. 

EMERSON,  Song  of  Nature. 

Vertebrates  and  Invertebrates.  However  various  in  form 
and  structure  the  members  of  the  phyla  thus  far  discussed 
are,  they  have  in  common  at  least  this  negative  character, 
that  in  none  of  them  has  a  backbone  been  developed.  For 
this  reason  they  are  collectively  termed  Invertebrates  (Lat. 
in,  not ;  vertebratm,  vertebrate) ;  the  animals  which  have  a 
backbone  are  called  Vertebrates.  It  will  be  worth  our  while, 
before  beginning  the  study  of  the  latter,  to  consider  some 
general  questions  of  interest  in  connection  with  the  evolution 
of  the  invertebrate  phyla,  and  then  to  describe  briefly  some 
peculiar  forms  which  appear  to  stand  between  the  inverte- 
brates and  the  vertebrates.  These  intermediate  forms,  or  their 
ancestors,  may  be  the  immediate  ancestors  of  the  vertebrates. 

THE  EVOLUTION  OF  THE  INVERTEBRATES 

Sources  of  Information.  There  are,  as  we  have  seen  in 
the  chapter  on  insects,  three  sources  of  information  which  the 
zoologist  may  draw  upon,  in  his  endeavor  to  discover  the  rela- 
tionship which  the  animals  of  the  past  and  the  present  evi- 
dently bear  to  each  other,  throughout  the  long  series  from 
the  lowest  to  the  highest.  These  sources  of  information  are 
the  geological  record  of  species,  comparative  anatomy  or 

292 


THE  EVOLUTION  OF  INVERTEBRATES         293 

morphology,  and  the  embryological   stages   in  the  develop- 
ment of  the  individual.    We  shall  consider  first  the  record  of 
geology,  and  in  order  to  do  this  intelligently  we  shall  have 
to  begin  far  back,  for  perhaps  more  than  any  other  science, 
geology  requires   of  the  mind  of  man  vast  sweeps   of  the 
imagination  to  form  even  faint  conceptions  of  the  illimitable 
processes  that  have  brought  the  earth  to  its  present  state. 
Scarcely  less  awe-inspiring  is  the  contemplation  of  the  changes 
that  must  have  taken  place  in  living  things,  since  life  began/ 
in  the  ocean  and  on  the  land.    Great  as  the  time  and  changesl! 
were  before  the  earth  had  life  upon  it,  greater  still  may  be^ 
the  time  that  the  processes   of  evolution  have  required  to  I 
develop  all  the  forms  of  life  in  their  complexity. 

The  Nebular  Hypothesis.  The  earth  is  one  of  a  number  of 
bodies  called  planets,  which  revolve  about  a  central  heated 
body,  the  sun.  The  planets,  with  their  attendant  moons  or 
satellites,  and  a  number  of  smaller  bodies  revolving  about  the 
sun  in  the  same  direction  and  nearly  in  the  same  plane,  con- 
stitute our  solar  system.  The  nebular  hypothesis  is  a  theory 
which  involves  the  suggestion  of  a  common  origin  for  all 
members  of  the  solar  system  from  a  mass  of  heated  gaseous 
material  (Lat.  nebula,  cloud)  in  motion,  which  is  supposed  to 
have  occupied  all  the  space  between  the  central  sun  and  the 
orbit  of  the  outermost  planet.  In  the  process  of  cooling  and 
condensation  rings  of  matter  were  formed,  which  later  broke 
up  into  the  different  planets. 

Archaean  Time.  The  earliest  period  of  the  earth's  geological 
history  is  termed  the  Archaean  Era  (Gr.  archaios,  ancient). 
At  first  all  the  substances,  including  the  water  which  now 
covers  three  quarters  of  the  earth's  surface,  were  held  sus- 
pended in  the  atmosphere,  owing  to  the  high  temperature. 
Later  there  came  a  time  when  the  waters  condensed,  and  the 
surface,  cooled  still  further,  permitted  the  water  to  cover 
the  rocks  of  the  early  crust  entirely  or  in  part.  Stupendous 


294 


GENERAL  ZOOLOGY 


volcanic  upheavals  must  have  been  frequent  as  fire  and  water 
struggled  for  the  mastery.  During  this  time,  of  course,  no 
life  was  possible.  As  the  crust  continued  to  cool  it  was 
upheaved  and  formed  land.  When  the  waters  had  cooled 
sufficiently  to  permit  of  it,  life  appeared,  but  in  what  form 


FIG.  146.  North  America  in  the  Archsean  Era 
(From  Dana's  Manual  of  Geology) 

we  do  not  know.  It  is  thought  that  this  early  life  may  have 
been  plant  rather  than  animal  in  its  nature,  since  plants 
to-day,  with  the  exception  of  the  fungi  (mushrooms,  bacteria, 
etc.),  feed  upon  mineral  matter,  while  animals  require  plant 
or  animal  food.  As  regards  the  temperature  at  which  life 
became  possible,  it  is  known  that  plants  live  now  in  the  hot 
springs  of  the  West  in  water  reaching  180°  F. 


THE  EVOLUTION  OF  INVERTEBRATES 


295 


There  is  very  little  direct  evidence  to  indicate  the  charac- 
ter of  the  life  in  the  Archaean  era,  but  in  all  probability  it 
was  of  the  simplest  structure,  like  some  of  the  single-cell 
organisms  of  to-day.  Although  fossil  remains  of  that  time  are 
wanting,  beds  of  limestone  and  graphite  formed  then,  point 
to  the  existence  of  life,  for  similar  beds  formed  in  later  eras 
are  known  to  have  been  made  through  the  agency  of  organ- 


FIG.  147.  North  America  toward  the  Close  of  the  Age  of  Invertebrates 
(From  Dana's  Manual  of  Geology] 

isms  (polyps,  mollusks,  etc.,  and  plants).  Fig.  146  shows  the 
North  American  continent  as  it  probably  existed  at  the  close, 
of  the  Archaean  era.  The  main  body  of  land  was  a  V-shaped 
mass  lying  north  of  the  present  Great  Lakes  and  the  St. 
Lawrence  River.  Archaean  islands  lay  in  the  position  of  parts 
of  subsequent  eastern  and  western  highlands. 

The  Age  of    Invertebrates.    Following   the   Archaean  era, 
several  succeeding  geological  periods  may  be,  for  our  purpose, 


296  GENERAL  ZOOLOGY 

grouped  under  the  general  term,  Age  of  Invertebrates,  from 
the  predominance  of  these  forms  of  life.  The  era  was 
very  long,  undoubtedly  to  be  reckoned  in  millions  of  years. 
We  have  no  knowledge  of  the  exact  time  that  the  different 
species  appeared,  nor  of  the  exact  length  of  time  they  existed. 
Neither  do  we  know  from  actual  specimens  all  the  stages  of 
evolution  through  which  the  early  forms  of  life  may  have 
passed  in  coming  to  the  form  and  structure  in  which  we 
know  their  kin  to-day,  for  the  intermediate  types  have  been 
lost  on  account  of  one  catastrophe  or  another  in  the  history 
of  the  world. 

In  the  beginning  of  the  era,  life  was  marine,  as  far  as  fossil 
records  indicate.  The  earliest  fossils  are  of  sponges,  corals, 
sea-lilies  or  crinoids  (see  p.  246),  worms,  brachiopods  (see 
p.  233),  mollusks,  and  trilobites  (see  p.  153).  Subsequently 
land  animals  made  their  appearance  in  forms  like  the  arach- 
nids and  the  insects.  Before  the  close  of  the  era  a  class  of 
vertebrate  animals,  the  fishes,  had  come  into  existence.  The 
accompanying  map  (Fig.  147)  will  give  an  idea  of  the  probable 
growth  of  the  land  area  of  North  America  during  the  period. 

Evidence  from  Embryology  and  Morphology.  Frequently 
the  only  way  the  zoologist  may  know  of  the  kinship  of  cer- 
tain groups  is  by  studying  their  early  stages  of  development. 
Since  all  the  animals  composed  of  more  than  one  cell  repro- 
duce at  one  time  or  another  by  means  of  eggs  and  sperma- 
tozoa, we  see  that  all  animals,  however  great  the  differences 
between  the  adults  may  be,  are  alike  in  being  composed  of 
one  cell  at  the  beginning  of  development.  But  in  some  ani- 
mals the  number  and  complexity  of  the  changes  intervening 
between  the  egg  stage  and  the  adult  stage  are  few  and  sim- 
ple in  comparison  with  the  changes  taking  place  in  others. 
All  those  animals  which  have  few  organs  show  relatively 
few  changes  in  development,  in  comparison  with  those 
animals  which  have  numerous,  complicated  organs.  Hydra, 


THE  EVOLUTION  OF  INVERTEBRATES         297 

for  example,  as  morphology  shows,  is  a  very  simple  form  com- 
pared with  the  earthworm.  Not  only  has  Hydra  fewer  organs 
than  the  earthworm,  but  reference  to  the  study  of  develop- 
ment of  the  latter  will  show  that  the  two  layers  of  cells 
which  constitute  the  entire  animal  Hydra  represent  a  very 
early  stage  in  the  development  of  the  earthworm. 

There  is  an  additional  point  of  value  to  be  observed  in 
the  comparison  of  Hydra  and  the  earthworm.  There  are  two 
phyla  of  animals  that  in  development  have  two  germ-layers,— 
Porifera  and  Coelentera.  All  the  others  (except  the  Protozoa) 
have  three  germ-layers.  The  third  germ-layer,  the  mesoderm, 
offers  a  beginning  place  for  organs  not  developed  in  the 
ectoderm  and  endoderm,  and  groups  of  animals  possessing  it 
develop  more  kinds  of  organs  than  those  which  do  not  have 
it ;  that  is  to  say,  they  show  greater  differentiation. 

If  we  were  to  begin  at  once  to  arrange  all  animals  in  a 
regular  graded  series,  on  the  basis  of  what  we  learn  from 
morphology  and  from  embryology,  we  should  have  a  difficult 
task.  The  number  of  facts  that  it  is  necessary  to  know  is  so 
considerable  that  even  to-day  systematic  zoologists  are  not 
agreed  on  important  details  of  grouping  animals  in  a  com- 
plete system  of  classification.  Besides,  the  doctrine  of  evolu- 
tion takes  into  account  the  fact  that  the  phyla  of  animals 
have  not  developed  in  a  direct  line,  but  as  branches  from  a 
previously  existing  stem.  The  whole  system  of  animals 
might  be  represented  graphically  by  a  series  of  stem  and 
branches  resembling  a  tree  ;  but  whereas  in  a  tree  we  can 
trace  down  one  branch  and  out  any  other,  in  the  diagram 
suggested  some  of  the  branches  would  not  be  connected  with 
the  stem  at  all,  because  the  organisms  which  would  stand  in 
the  connecting  places  have  disappeared  both  in  living  and 
in  fossil  form. 

However,  we  can  see  very  clearly  that  the  Protozoa  being 
composed  of  a  single  cell  are  the  lowest  of  all  animals ;  and 


298  GENERAL  ZOOLOGY 

that  the  Porifera,  with  their  structure  showing  no  sign  of 
digestive  organs,  muscle-cells,  nerve-cells,  or  sense-organs,  are 
the  simplest  of  the  many-cell  animals  (Metazoa).  Of  course 
we  do  not  place  the  Porifera  next  above  the  Protozoa  until 
we  have  weighed  the  facts  by  comparing  their  structure  with 
the  only  other  phylum  that  has  two  germ-layers.  The  Cce- 
lentera  have,  as  we  recall,  a  gastrovascular  cavity,  simple 
muscle-cells,  nerve-cells,  and  sense-organs. 

An  attempt  to  classify  the  animals  that  have  three  germ- 
layers  in  development  immediately  brings  us  into  difficulties. 
Formerly  it  was  the  custom  to  place  the  Echinoderma  near 
the  Ccelentera  because  of  their  radiate  plan  of  structure,  but 
now  the  radial  symmetry  is  not  generally  considered  a  factor 
of  great  significance.  The  old  group  of  Venues  has  been  thor- 
oughly studied  in  recent  years,  and,  as  indicated  in  Chapter 
XVII,  it  has  been  subdivided  into  five  phyla  by  some  of  the 
best-known  authorities.  In  the  order  of  their  increasing  com- 
plexity, the  phyla  are  Platyhelminthes,  Nemathelminthes, 
Trochelmiiithes,  Molluscoida,  and  Annulata.  They  are  all 
bilaterally  symmetrical  animals,  but  only  the  last  phylum  has 
the  body  divided  into  somites.  Because  of  this  and  other 
facts,  the  order  of  classification  is  modified  by  the  English 
zoologists  Parker  and  Haswell  by  placing  the  Echinoderma 
between  the  Molluscoida  and  the  Annulata.  The  Echino- 
derma have  an  alimentary  canal  separated  from  the  body- 
cavity,  digestive  glands,  a  fairly  well-defined  blood-system, 
an  elaborate  water-vascular  system,  and  a  definite  nervous 
system.  For  these  reasons  they  are  entitled  to  rank  next  to 
the  Annulata.  All  members  of  the  Annulata  have  the  body 
divided  into  somites  with  unsegmented  appendages.  The 
body  has  a  distinct  alimentary  canal,  a  complete  blood-system, 
and  a  more  complicated  nervous  system  than  is  found  in  any 
of  the  phyla  already  mentioned.  The  system  of  nephridia  also 
is  more  extended,  one  pair  being  present  in  every  somite. 


THE  EVOLUTION  OF  INVERTEBRATES         299 

The  phylum  Arthropoda  is  pretty  clearly  distinct  from 
other  phyla.  Its  advance  over  the  Annulata  consists  in  the 
tendency  of  the  somites  to  be  fewer  and  more  definite  in 
number.  The  somites  are  grouped  in  two  or  three  regions; 
in  certain  regions  the  somites  are  fused,  an  indication  of  still 
greater  differentiation.  All  the  appendages  are  segmented. 
The  dorsal  blood-vessel  is  more  differentiated  than  other 
parts  of  the  circulatory  system,  and  in  some  classes  it  is  a 
clearly  defined  one-chambered  heart.  Sense-organs,  especially 
eyes,  reach  a  condition  of  great  complexity  in  comparison 
with  what  is  found  in  lower  phyla. 

If  division  into  somites  is  an  indication  of  advance,  the 
loss  of  it  would  seem  to  be  an  indication  of  degeneration,  but 
we  have  no  proof  that  the  ancestors  of  the  Mollusca  had 
bodies  which  showed  metamerism.  Their  development  was 
evidently  in  a  different  direction  from  that  of  the  Annulata 
and  the  Arthropoda.  The  factors  which  seem  to  place  Mol- 
lusca higher  in  the  system  are  greater  centralization  of  the 
nervous  system  in  a  miniature  "brain,"  and  the  possession 
of  a  three-chambered  heart,  —  two  auricles  and  one  ventricle. 

INVERTEBRATE  PHYLA  AND  CLASSES 

The  subjoined  list  of  the  classes  discussed  in  the  first 
twenty-one  chapters  will  be  of  service  in  recalling  the  rela- 
tive position  of  the  phyla  in  the  system  of  classification. 

I.  PROTOZOA 

Class  1.   Sarcodina;  example,  Amoeba  protens. 
Class  2.  Mastigophora  ;  example,  Euglena  viridis. 
Class  3.   Sporozoa;  example,  Plasmodium  malariae. 
Class  4.  Infusoria  ;  example,  Paramoecium  caudatum. 

II.  PORIFERA 

Class  1.  Porifera;  example,  Heteromeyenia  ryderi. 


300  GENERAL  ZOOLOGY 

ITT.    C<ELENTERA 

Class  1.   Hydrozoa  ;  example,  Hydra  viridis. 
Class  2.  Scyphozoa  ;    example,  Aurelia  flavidula. 
Class  3.  Actinozoa ;   example,  Metridium  raarginatum. 
Class  4.  Ctenophora  ;  example,  Pleurobrachia  rhododactyla. 

IV.  PLATYHELMINTHES 

Class  1.  Turbellaria  ;  example,  Dendrocoelum  lacteum. 
Class  2.   Trematoda;  example,  Distomum  somaterise. 
Class  3.  Cestoda ;  example,  Taenia  saginata. 

V.  NEMATHELMINTHES 
Class  1.  Nematoda;  example,  Trichina  spiralis. 

YT.  TROCIIELMINTHES 

Class  1.  Rotifera ;  example,  Brachionus  urceolaris. 

YTT.  MOLLUSCOIDA 

Class  1.   Polyzoa  ;  example,  Plumatella  repens. 
Class  2.  Brachiopoda  ;  example,  Lingula  lepidula. 

YTIT.    ECHINODERMA 

Class  1.  Asteroidea ;  example,  Asterias  vulgaris. 

Class  2.  Ophiuroidea ;  example,  Astrophyton  agassizii. 

Class  3.  Echinoidea  :  example,  Strongylocentrotus  drobachiensis. 

Class  4.  Holothuroidea  ;  example,  Cucumaria  chronhjelmi. 

Class  5.  Crinoidea;  example,  Pentacrinus  blakei. 

IX.  ANNULATA 

Class  1.   Chsetopoda;  example,  Lumbricus  terrestris. 
Class  2.   Hirudinea  ;  example,  Placobdella  rugosa. 

X.  ARTHROPODA 

Class  1.  Crustacea;  example,  Cambarus  affinis. 
Class  2.  Xiphosura;  example,  Limulus  polyphemus. 
Class  3.  Arachnida ;  example,  Argiope  riparia. 
Class  4.  Myriapoda;  example,  Lithe-bins  americanus. 
Class  5.  Hexapoda ;  example,  Melanoplus  femur-rubrum. 


THE  EVOLUTION  OF  INVERTEBRATES 

XI.    MOLLUSCA 

Class  1.  Pelecypoda ;  example,  Mya  arenaria. 
Class  2.  Gasteropoda ;  example,  Helix  nebulosa. 
Class  3.  Cephalopoda;  example,  Nautilus  pompilius. 


301 


PROBABLE  ANCESTORS  OF  THE  VERTEBRATES 

The  Lancelet.  It  is  always  important  to  find,  if  possible, 
connecting  links  between  large  and  seemingly  distinct  groups 
of  animals.  The  words  "  invertebrate  "  and  "  vertebrate  " 
were  once  thought  to  be  terms  which  together  included  all 
animals ;  but  zoologists  have  discovered  several  animals 
which  are  neither  vertebrate  nor  invertebrate  in  the  usual 
sense  of  the  words. 

The  first  of  the  three  animals  to  be  described  in  this  sec- 
tion of  the  chapter  is  a  vertebrate  of  a  very  simple  type. 


FIG.  148.  The  Lancelet.  x  2.    (After  Kowalevsky) 

1,  mouth;  2,  gill-slits;  3,  atrium;  4,  atrial  pore;  5,  intestine;  6,  anus;  7,  noto- 
chord;  8,  nerve-cord 

The  lancelet  (Amphiox'us  lanceola'tus,  Fig.  148)  is  a  fish-like 
animal  about  two  inches  long.  It  lives  almost  imbedded  in 
the  sand  at  the  sea-bottom  in  Chesapeake  Bay  and  in  other 
warm  ocean  waters. 

The  mouth  (Fig.  148,  1)  of  the  lancelet  opens  into  a  long 
pharynx,  which  has  many  pairs  of  gill-slits  (Fig.  148,  2). 
When  water  and  food  pass  in  at  the  mouth,  the  water  passes 
through  the  gill-slits,  giving  up  oxygen  to  the  blood  in  the 
gills,  and  then  passes  into  a  chamber  partially  surrounding 
the  pharynx,  called  the  atrium  (Fig.  148,  3),  and  to  the 


302 


GENERAL  ZOOLOGY 


outside  by  the  atrial  pore  (Fig.  148,  4) ;  the  food  goes  down 
the  intestine  (Fig.  148,  5). 

Immediately  above  the  intestine  is  the  structure  which 
corresponds  in  position  to  the  backbone  of  higher  animals  ; 
it  is  called  the  notochord  (Fig.  148,  7).  The  notochord  is  soft 
throughout  life,  but  it  is  sufficiently  strong  to  act  as  a  support- 


B— ' 


FIG.  149.   Photograph  of  Living  Tunicates.    Natural  size 
A,  Styela  stimpsoni ;  Z>,  Cynthia  haustor 

ing  skeleton  for  the  body.  Parallel  with  the  notochord  and 
above  it,  is  the  spinal  cord  (Fig.  148,  8)  lying  near  the  dorsal 
wall.  The  characteristics  of  structure  which  make  Amphioxus 
a  vertebrate  are  the  presence  of  gill-slits,  a  notochord  above 
the  intestine,  and  a  spinal  cord  dorsal  to  the  notochord. 

The  Sea-Squirt.  As  far  as  outward  appearance  indicates  the 
sea-squirts,  Sty'ela  stimpson'i  and  Cyn'thia,  haus'tor  (Fig.  149, 


THE  EVOLUTION  OF  INVERTEBRATES 


303 


A  and  Z?),  have  nothing  in  common  with  vertebrates.  Sea- 
squirts  live  attached  to  rocks  and  wharves,  and  once  attached 
never  leave  the  place.  The  body 
is  covered  with  a  tough  coat  or 
tunic,  which  gives  the  class  its 
name,  Tunica1  ta.  The  food  and 
oxygen  are  drawn  through  the 
opening  in  the  upper  tube,  and 
the  excess  water  and  wastes  are 
discharged  by  the  lower  tube. 
There  is  a  pharynx  Avith  gill- 
openings,  and  a  nervous  system, 
but  there  is  no  indication  of  a 
notochord. 

The  adult  tunicate  exhibits 
a  lower  degree  of  organization 
than  the  larva.  The  larva  (Fig. 
150)  has  very  much  the  form 
of  a  frog-tadpole,  and  it  swims 
about.  Its  locomotor  organ  is  a 
fin-like  tail  (Fig.  150,  12).  As 
long  as  the  animal  remains  a 
larva  it  has  structures  which 
indicate  vertebrate  relationship. 
Extending  through  the  middle 
of  the  tail  is  a  notochord  (Fig. 
150,  6),  which  is  evidently  a  sup- 
porting organ.  Dorsal  to  the 
notochord  is  the  nerve-cord  (Fig. 
150,  7).  Below  the  notochord  is 
the  alimentary  canal  (Fig.  150,  3),  and  near  by  are  the  begin- 
nings of  the  gills,  with  openings  (Fig.  150,  2)  which,  however, 
are  not  gill-slits.  When  the  larva  reaches  a  certain  stage  of 
development,  it  fastens  itself  by  adhesive  papilla?  (Fig.  150, 11) 


11 


FIG.  150.  Larva  of  Tunicate. 
Much  enlarged.  (After  Herd- 
in  an) 

1,  incurrent  opening ;  2,  gill-open- 
ings ;  3,  intestine ;  4,  anus ;  5,  ex- 
current  opening  ;  6,  notochord  ; 
7,  nerve-cord  ;  8,  eye ;  9,  otocyst ; 
10,  endostyle;  11,  adhesive  pa- 
pillae; 12,  portion  of  tail 


304 


GENERAL  ZOOLOGY 


to  some  fixed  object.  Then  begins  the  process  of  degener- 
ation of  all  distinctly  vertebrate  structures ;  the  tail  is 
absorbed,  the  notochord  also  disappears,  and  the  nerve-cord 
changes  form.  If  it  were  not  for  what  is  known  of  the 

larva,  the  vertebrate  relationship  of 
tunicates  would  never  be  suspected. 
The  Acorn-Tongue  Worm.    Some 
zoologists    have    supposed    that    the 
ancestors  of  the  vertebrates  were 
worm-like  animals.     The  reasons  for 
that  supposition  are  based  chiefly  on 
3    the   structure   of   the   acorn-tongue 
worm,  Balanoglos'sus  (Fig.  151).   This 
animal  is  found  in  the  sand  of  sea- 
shores.   It  has  a  proboscis  (Fig.  151,  l) 
with  a  collar-like  band  (Fig.  151,  2)  at 
the  base,  both  Organs  together  some- 
what resembling  an  acorn  in  its  cup. 
The  mouth,  at  the  base  of  the 
proboscis,  opens  into  a  pharynx  from 
which   many   pairs   of  gill-slits  (Fig. 
151,  3)  open  to  the  exterior.  There  is 
a  dorsal  nerve-cord  and  a  ventral  nerve- 
FIG.  151.   Acorn-Tongue    cord.    A  notochord-like  structure  has 
Worm.  Enlarged.   (After    ^       f         d  extending  into  the  middle 
A.  Agassiz)  &  . 

ot  the   proboscis.     Many  zoologists 

1,  proboscis ;  2,  collar ;  3,  gill-  ,       ,  ,  .    *     , ,  . 

slits  express  doubt  concerning  this  organ, 

and  no  investigator  seems  to  be  posi- 
tive of  its  notochordal  structure.  If*  the  .main  nerve-cords 
were  limited  to  one  above  the  intestine,  that  would  clearly 
be  a  vertebrate  characteristic ;  but  with  one  above  and  one 
below,  it  is  neither  definitely  vertebrate  or  invertebrate,  and 
hence  possibly  an  intermediate  form.  The  gill-slits  have  the 
position  and  form  of  those  in  Amphioxus. 


CHAPTER  XXIII 
THE  YELLOW  PERCH 

Give  me  some  observations  and  directions  concerning  the  Pearch  for  they 
say  he  is  both  a  very  good  and  a  bold  biting  fish,  and  I  would  fain  learne 
to  fish  for  him.  — IZAAK  WALTON,  The  Complete  Angler. 

Habitat  and  Distribution.  Brilliant  in  coloration,  abundant 
and  easy  of  capture,  and  possessing  a  firm,  white  flesh  of 
delicate  flavor,  it  is  no  wonder  that  the  yellow  perch  (Per'ca 
flaves'cens,  Fig.  152)  is  one  of  the  best  known  of  the  fresh- 


FIG.  152.  Photograph  of  Yellow  Perch.    Reduced 
(From  Jordan  and  Evermann's  American  Food  and  Game  Fishes) 

water  fishes  of  the  United  States.  Though  found  in  streams, 
especially  in  those  with  quiet  reaches  of  water,  the  yellow 
perch  is  more  truly  a  creature  of  ponds  and  lakes.  There  it 
prefers  a  pebbly  or  sandy  bottom.  Its  range  extends  from 
Labrador  to  Georgia  in  the  fresh-water  rivers  and  the  lakes 

305 


306  GENERAL  ZOOLOGY 

along  the  Atlantic  coast,  and  westward  in  the  region  of  the 
Great  Lakes  and  upper  Mississippi  valley.  Though  origi- 
nally absent  from  the  far  West,  it  has  recently  been  intro-- 
duced  with  success  into  the  lakes  of  Washington,  Oregon, 
and  California.  In  structure  and  habits  our  yellow  perch 
very  closely  resembles  the  perch  of  Europe,  referred  to  in  the 
quotation  at  the  head  of  this  chapter,  and  by  some  authors 
it  is  considered  to  be  identical  with  the  latter  species. 

External  Structure.  The  body  of  the  perch  is  elongate, 
slightly  compressed  from  side  to  side,  and  tapers  toward  both 
ends.  Three  divisions  are  apparent,  the  head,  trunk,  and  tail; 
several  appendages,  the  fins,  are  attached  to  the  body.  The 
covering  is  a  smooth  skin,  containing  pigment  cells,  to  which 
the  colors  are  due,  and  glands  which  secrete  mucus.  Within 
pouches  in  this  skin  are  transparent  scales,  which  overlap, 
like  the  shingles  on  the  roof  of  a  house,  and  form  a  coat  of 
mail,  incasing  the  fish  from  head  to  tail.  Along  a  clearly 
defined  lateral  line  the  scales  are  somewhat  modified,  and 
beneath  them  are  sense-organs  the  functions  of  which  have 
been  variously  stated.  Professor  G.  H.  Parker  considers  that 
these  organs  are  sensitive  to  mechanical  jars  of  a  low  rate  of 
frequency,  thus  standing  between  organs  of  touch  proper,  and 
those  of  hearing. 

At  the  anterior  end  of  the  head  are  the  jaws,  armed  with 
teeth  for  seizing  food.  The  eyes  have  no  eyelids.  Just  in 
front  of  the  eyes  are  the  nostrils,  two  on  either  side.  They 
have  no  communication  with  the  mouth.  Behind  the  eyes,  on 
each  side  of  the  body,  is  a  movable  flap  called  the  operculum, 
beneath  which  are  the  red  comb-like  gills.. 

There  are  five  fins,  three  unpaired  and  two  in  pairs.  Of  the 
unpaired  fins  those  on  the  back  are  called  the  dorsal  fins,  the 
one  on  the  under  side  the  anal  fin,  and  the  one  at  the  tail 
the  caudal  fin.  The  more  anterior  of  the  paired  fins  are  the 
pectoral  fins ;  the  more  posterior  and  lower,  the  ventral  or 


THE  YELLOW  PERCH  307 

pelvic  fins.  The  fins  are  supported  by  Jin-rays  of  two  sorts, 
the  one  hard,  unsegmented,  and  unbranched  (Fig.  153,1);  the 
other  soft,  segmented,  and  branched  (Fig.  153,  2). 

The  Digestive  System.  The  mouth  is  large.  Teeth  are  borne 
not  only  on  the  jaws  but  also  on  the  roof  of  the  mouth 
(Fig.  153,  6,  7,  9).  On  the  ventral  surface  of  the  mouth  is  a 
rather  large,  fleshy  tongue  (Fig.  153,  8).  Behind  the  tongue 
is  the  pharynx  (Fig.  153,  10),  with  gill-slits  on  both  sides, 
which  allow  water  from  the  mouth  to  pass  into  the  gill-cham- 
ber. From  the  pharynx  a  short  oesophagus  leads  to  the  stomach 
(Fig.  153,  14).  Several  pyloric  cceca  (Fig.  153,  15)  open  into 
the  intestine  (Fig.  153,  16),  increasing  its  absorbing  and  secret- 
ing surface.  The  intestine  ends  ventrally  at  the  anal  opening 
anterior  to  the  anal  fin  (Fig.  153,  4).  The  liver-secretion, 
called  bile,  is  stored  in  a  gall-bladder  (Fig.  153,  12)  attached 
to  the  posterior  surface  of  the  liver  (Fig.  153,  11),  and  finds 
its  way  into  the  alimentary  canal  through  the  bile-duct  (Fig. 
153,  13).  Close  to  the  alimentary  canal,  but  not  opening  into 
it,  is  a  bright  red  organ  called  the  spleen  (Fig.  153,  20),  the 
function  of  which  is  not  positively  known. 

The  Circulatory,  Respiratory,  and  Excretory  Systems.  The 
heart  is  placed  in  a  large  pericardial  cavity,  the  posterior  wall 
of  which  forms  a  thin  membrane  separating  the  heart  from  the 
other  organs  of  the  body-cavity.  Two  divisions  to  the  heart 
may  be  clearly  distinguished,  an  auricle  (Fig.  153,  21)  and  a 
ventricle  (Fig.  153,  22).  The  blood,  driven  from  the  heart  by 
the  contraction  of  the  ventricle,  is  forced  through  an  artery 
(the  aorta]  with  a  bulbous  base  (bulbus  aorta;,  Fig.  153,  23)  to 
the  gills,  where  it  is  aerated.  After  aeration  the  blood  is 
collected  into  a  dorsal  artery,  which  carries  it  through  the 
bodjr,  giving  off  branches  to  the  various  organs.  In  the 
capillaries  of  the  different  organs  it  gives  up  its  oxygen,  col- 
lects waste  products,  and  makes  its  way  through  the  veins 
to  the  auricle,  whence  it  enters  the  ventricle  to  repeat  its 


308  GENERAL  ZOOLOGY 

circulation.  Valves  in  the  heart  and  in  the  course  of  the  venous 
circulation  prevent  the  backward  flow  of  the  blood.  In  addi- 
tion to  the  blood,  a  white  fluid  (lymph)  circulates  through 
the  body  in  vessels  called  lymphatics.  The  function  of  the 
lymph  is  supplementary  to  that  of  the  blood. 

The  principal  organs  of  respiration  are  the  gills,  eight  in 
number,  four  on  either  side.  Each  gill  consists  of  a  bony 
arch,  on  the  anterior  surface  of  which  are  teeth-like  gill- 
rakers  ;  on  the  posterior  surface  are  the  delicate  gill-filaments. 
In  this  position  the  filaments  are  constantly  bathed  by  a  cur- 
rent of  water,  which  passes  from  the  mouth-cavity  out  beneath 
the  operculum.  In  the  dorsal  part  of  the  body-cavity  is  a 
large  air-bladder  (Fig.  153,  19).  In  the  lining  of  the  wall  of 
the  air-bladder  is  a  network  of  blood-vessels,  grouped  into 
gland-like  "  red  bodies."  By  the  absorption  and  formation 
of  gas  by  these  blood-vessels  the  weight  of  the  fish  can  be 
maintained  nearly  equal  to  that  of  the  water  it  displaces. 
The  air-bladder  is  probably  useful  also  as  a  reservoir  of  air, 
for  it  has  been  found  that  in  a  perch  suffocated  in  stagnant 
water  the  oxygen  in  the  air-bladder,  which  normally  amounts 
to  about  one  fifth  of  the  volume  of  the  inclosed  gas,  had 
been  entirely  absorbed  and  replaced  by  carbon  dioxide  and 
nitrogen.  In  some  fishes  the  air-bladder  communicates  with 
the  alimentary  canal  by  means  of  a  tube  called  the  pneumatic 
duct.  In  the  perch  this  duct  is  present  in  early  life,  but  it 
soon  closes,  remaining,  however,  as  a  fibrous  cord  (Fig.  153, 18). 

The  perch,  like  other  fishes,  is  usually  spoken  of  as  cold- 
blooded, since  its  body-temperature  is  little  above  that  of  the 
surrounding  medium.  Compared  with  the  higher  vertebrates, 
the  birds,  for  example,  very  little  oxygen  is  required  for 
respiration,  and  the  circulation  is  comparatively  slow. 

The  principal  organs  of  excretion  are  the  M^j/s(Fig.l53,24), 
placed  just  above  the  air-bladder  and  below  the  back-bone. 
From  the  kidneys  two  tubes,  the  ureters  (Fig.  153,  25),  lead, 


309 


310  GENERAL  ZOOLOGY 

after  union,  to  the  urinary  bladder  (Fig.  153,  26).  The  con- 
tents of  the  urinary  bladder  are  carried  to  the  surface  of  the 
body  at  the  urinogenital  opening  (Fig.  153,  37),  just  posterior 
to  the  anal  opening. 

The  Skeletal  System.  So  far  in  our  study  of  the  animal 
kingdom  the  skeletal,  or  protecting  and  supporting,  parts  have 
been  found  chiefly  on  the  outside ;  in  the  fish  there  is  a  well- 
developed  internal  skeleton  formed  of  bones  composed  largely 
of  phosphate  of  lime.  Running  from  head  to  tail  through  the 
body  is  the  back-bone  or  vertebral  column,  consisting  of  a 
number  of  separate  bones  called  vertebrae  (Fig.  153,  27),  and 
continued  into  a  brain-case  or  cranium  (Fig.  153,  28)  at  the 
anterior  end.  Bones  also  form  the  foundation  of  the  upper 
and  lower  jaws,  and  support  the  gills  and  tongue.  Attached 
to  the  back-bone  are  a  number  of  ribs  which  inclose  and  pro- 
tect the  organs  of  the  body-cavity.  A  row  of  small  bones 
(interspinals,  Fig.  153,  29)  supports  the  unpaired  fins.  The 
pectoral  and  ventral  fins  are  each  supported  by  a  framework 
of  bones  forming  respectively  a  shoulder-girdle  and  a  hip  or 
pelvic  girdle. 

The  Nervous  and  Muscular  Systems.  Four  divisions  are  quite 
clearly  marked  in  the  brain,  —  the  cerebrum  (Fig.  153,  32); 
the  two  large  rounded  optic  lobes  (Fig.  153,  33)  ;  the  medially 
and  dorsally  placed  cerebellum  (Fig.  153,  34) ;  and  the  medulla 
oblongata,  the  latter  tapering  posteriorly  into  the  spinal  cord 
(see  Fig.  153,  where  the  medulla  is  shown  though  not  num- 
bered). Anteriorly  the  brain  is  prolonged  into  the  olfactory 
tracts  (Fig.  153,  30),  which  communicate  with  the  nostrils  ; 
nerves  extend  to  the  different  sense-organs  and  to  the  various 
parts  of  the  body. 

The  ears  of.  the  perch  consist  of  two  closed  cavities  on 
opposite  sides  of  the  cranium,  containing  concretions  of  car- 
bonate of  lime,  called  otoliths,  or  ear-stones.  There  has  been 
some  question  in  the  past  as  to  whether  fishes  could  hear, 


THE  YELLOW  PERCH 


311 


but  recent  experiments  seem  to  show  that  some,  at  least,  are 
capable  of  appreciating  sound- vibrations.  The  ears  also  serve 
as  organs  of  equilibration,  by  aid  of  which  the  fish  is  able  to 
maintain  its  balance.  The  sense  of  touch  is  located  in  the 
skin  generally,  and  in  the  lateral-line  organs.  The  sense  of 
taste  is  not  greatly  developed  in  the  perch,  and  the  eyes 
are  not  adapted  for  vision  at  any  great 
distance.  The  organ  of  smell  of  fishes  is 
peculiar  among  vertebrates  in  that  it  has 
no  connection  with  the  respiratory  system. 

The  muscular  system  con- 
sists principally  of  a  long, 
thick  muscle  on  either  side, 
stretching  from  head  to  tail. 
In  the  young  fish  this  muscle 
is  divided  into  muscular  seg- 
ments extending  vertically 
and  corresponding  in  number 
with  the  vertebrae.  As  the 
young  fish  begins  active  exist- 
ence the  muscle-segments  are  Fi«.  154.  Eggs  of  Perch  before  and 
bent  and  twisted  so  that  for 
a  portion  of  their  extent  they 
seem  to  run  zigzag. 

The  Reproductive  System.  Both  the  ovary  of  the  female 
(Fig.  153,  36)  and  the  spermaries  of  the  male  are  of  large  size 
in  the  mature  perch.  They  open  on  to  the  surface  at  the 
urinogenital  opening  (Fig.  153,  37). 

Development.  Early  in  the  spring  the  adult  perch,  which 
have  spent  the  winter  in  the  deepest  waters  of  ponds  or  lakes, 
often  without  feeding  very  much,  draw  toward  the  shore. 
The  colors,  especially  on  the  males,  begin  to  brighten,  till  an 
adult  perch  in  the  full  glory  of  his  breeding  colors  is  one 
of  the  most  beautiful  objects  in  his  domain.  The  time  of 


after  Egg-Laying.    Reduced 

(From  Bulletin  United  States  Fish  Com- 
mission) 


312  GENERAL  ZOOLOGY 

spawning  varies  with  the  climate ;  in  the  South  it  begins  as 
early  as  March ;  in  New  England,  in  May.  The  eggs  are  laid 
in  shallow  water  in  a  ribbon-like  mass,  which,  after  absorption 
of  water,  is  sometimes  six  or  seven  feet  long  and  two  inches 
in  diameter.  This  great  mass,  which  contains  thousands  of 
eggs  (over  a  hundred  thousand  have  been  counted  irr  a  two- 
pound  perch),  is  fertilized  by  the  male  emitting  his  sperm 
(milt)  over  it.  The  eggs  form  a  large  part  of  the  food  of 
other  fishes  and  aquatic  birds,  and  were  it  not  for  their  great 
numbers  few  would  ever  hatch.  In  from  two  to  four  weeks, 
depending  on  the  temperature,  the  young  perch  hatches  from 
the  egg,  at  first  with  the  yolk-sac  attached  to  the  ventral  sur- 
face (compare  Fig.  155).  After  absorption  of  the  yolk-sac, 

which  soon  occurs,  the  young 
perch  differs  from  the  adult 
chiefly  in  its  smaller  size  and 
lighter  color,  and  in  the  rela- 
tively greater  size  of  head 
FIG.  155.  Young  Sturgeon  with  Yolk-  -,  n  .^  ,, 

Sac.    Enlarged.    (After  Ryder)          and  eyes  as  compared  With  the 

rest  of  the  body. 

Relation  to  Environment.  The  whole  organization  of  the 
perch  marks  it  at  once  as  one  of  the  predatory  type  of  ani- 
mals, —  those  which  hunt  their  food  and  depend  upon  their 
superior  strength  or  agility  to  obtain  it.  As  Izaak  Walton 
long  ago  said  of  its  European  relative,  the  yellow  perch  is 
"  one  of  the  fishes  of  prey  that,  like  the  Pike  and  Trout,  car- 
ries his  teeth  in  his  mouth,  not  in  his  throat,  and  dare  venture 
to  kill  and  devour  another  fish."  The  shape  of  the  body  is  pre- 
cisely that  which  offers  least  resistance  to  motion  in  the  water. 
The  strong  lateral  muscles  afford  an  economical  method  of 
applying  power  for  propulsion  to  the  caudal  fin,  which,  by  a 
slight  lateral  motion,  drives  the  fish  forcibly  forward.  Lateral 
and  median  fins  assist  in  maintaining  equilibrium,  in  steering, 
and  in  raising  and  lowering  the  fish  in  the  water. 


THE  YELLOW  PERCH  313 

The  colors  of  most  fishes  are  protective  in  their  nature, 
and  the  perch  is  no  exception  to  this  general  rule.  From 
above,  the  olivaceous  back  is  with  difficulty  distinguished 
from  the  water  itself  or  the  bottom  below ;  from  beneath,  the 
white  under  parts  are  colored  like  the  surface  of  the  water 
or  the  atmosphere  above.  The  mottled  sides  also  serve  to 
render  the  perch  less  conspicuous  in  an  environment  of  lights 
and  shadows  among  weeds  and  rocks  on  the  bottom.  It  has 
been  noted  that  in  some  instances  where  perch  live  both  in 
a  large  lake  and  in  its  tributaries,  as  in  Lake  Michigan  and 
the  rivers  which  flow  into  it,  the  lake  fish  have  a  tendency  to 
lighter  general  coloration  and  to  disappearance  of  the  dark 
vertical  bands.  It  has  been  suggested  that  this  difference  in 
color  is  due,  in  part  at  least,  to  the  smaller  amount  of  light, 
combined  with  the  absence  of  dark  lurking-places. 

The  study  of  the  mental  organization  of  the  perch  is  beset 
with  many  difficulties,  though  it  is  of  the  greatest  interest 
for  the  light  it  may  throw  on  problems  connected  with  the 
mental  life  of  the  higher  animals;  for  the  perch  is  a  member 
of  the  class  of  fishes,  one  of  the  oldest  and  most  generalized 
of  the  vertebrates,  to  which  division  man  himself  belongs. 
Perch  are  able  to  learn,  and  they  profit  by  experience,  even 
though  the  line  along  which  education  can  take  place  is  very 
narrow.  In  order  to  test  their  capacity  to  learn,  two  adult 
perch  were  kept  in  an  aquarium  in  which  a  glass  partition 
was  placed  several  times  a  week  for  a  period  of  about  a 
month.  Live  minnows  were  introduced  on  the  opposite  side 
of  the  partition  at  the  times  of  experimentation.  Of  course 
the  perch  bumped  their  noses  against  the  glass  in  a  vain 
attempt  to  get  at  the  food  temptingly  displayed  at  so  short 
a  distance.  After  they  had  become  accustomed  to  this  reac- 
tion, whenever  they  made  a  movement  in  the  direction  of 
the  minnows,  the  glass  partition  was  removed,  and  they 
were  watched  to  see  if  by  their  actions  they  seemed  to  recall 


314  GENERAL  ZOOLOGY 

the  effect  which  had  invariably  followed  a  movement  in  the 
direction  of  the  minnows.  On  the  whole,  the  observer  con- 
cluded that  the  perch  showed  strong  symptoms  of  having 
learned  to  appreciate  the  presence  of  an  obstacle,  for  neither 
fish  made  a  move  in  the  direction  of  the  minnows  when  the 
partition  was  first  removed.  The  same  observer  noted  that 
perch  are  very  imitative,  a  series  of  motions  on  the  part  of 
one  being  very  likely  to  be  performed  by  others.  This  is  prob- 
ably of  use  in  connection  with  their  gregarious  life,  where 
the  "  school  "  is  kept  together  by  each  fish  watching  and  fol- 
lowing the  others. 

Sight  is  probably  the  best  developed  sense,  though,  as 
already  stated,  the  eyes  are  not  adapted  to  vision  at  a  great 
distance.  To  test  the  power  of  sight  discrimination,  the  ob- 
server quoted  above  dropped  into  the  aquarium  pieces  of 
wireworms  (larvae  of  click-beetles)  alternately  with  similar  bits 
of  earthworms.  Nearly  every  time  one  or  more  of  the  bits 
of  wireworm  were  seized  by  the  perch,  only  to  be  dropped 
a  moment  later.  The  fishes  did  not  seem  to  make  any  per- 
manent association  between  the  appearance  of  the  wireworm 
and  its  inedible  character. 

Perhaps  the  clearest  way  to  picture  the  limitations  in 
the  mental  organization  of  a  fish  is  to  sum  up,  as  Professor 
Sanford  does,  some  characters  in  which  the  fish  differs  from 
man.  "No  fish  is  ever  conscious  of  himself;  he  never  thinks 
of  himself  as  doing  this  or  that,  or  feeling  in  this  way  or  that 
way.  The  whole  direction  of  his  mind  is  outward.  He  has 
no  language  and  so  cannot  think  in  verbal  terms ;  he  never 
names  anything  ;  he  never  talks  to  himself.  As  Huxley  says 
of  the  crayfish,  he  i  has  nothing  to  say  to  himself  or  any  one 
else.'  He  does  not  reflect;  he  makes  no  generalizations.  All 
his  thinking  is  in  the  present  and  in  concrete  terms.  He  has 
no  voluntary  attention,  no  volition  in  the  true  sense,  no  self- 
control." 


THE  YELLOW  PERCH  315 

The  food  of  the  young  perch  at  first  consists  entirely  of 
small,  delicate  crustaceans,  such  as  Cyclops  and  its  allies; 
from  the  time  the  perch  are  about  an  inch  and  a  half  in  length 
they  begin  to  add  insects  to  the  bill  of  fare.  Adult  perch  have 
a  still  more  varied  diet,  consisting  of  the  larger  crustaceans, 
mollusks,  and  other  fishes.  The  young  are  gregarious,  and 
those  of  about  the  same  size  tend  to  keep  together,  so  that 
every  farmer  boy  knows  his  chances  of  catching  "a  big  one" 
are  small  indeed  when  he  has  his  hook  in  a  swarm  of  little 
fishes.  He  has,  however,  this  consolation,  —  that  the  supply 
of  the  one  size  is  likely  to  last ;  for 

Perch,  like  the  Tartar  clans,  in  troops  remove, 
And,  urged  by  famine  or  by  pleasure,  rove  ; 
But  if  one  prisoner,  as  in  war,  you  seize, 
You  '11  prosper,  master  of  the  camp,  with  ease 
For,  like  the  wicked,  unalarmed  they  view 
Their  fellows  perish,  and  their  path  pursue. 

OPPIAN,  Halieutica. 


CHAPTER   XXIV 
THE  ALLIES  OF  THE  PERCH :  PISCES 

Halcyon  prophecies  come  to  pass 
In  the  haunts  of  bream  and  bass. 

MAURICE  THOMPSON. 

Definition  of  Pisces  (L&t. piscia,  a  fish).  The  perch  is  a  mem- 
ber of  the  class  Pis'ces.  Fishes  are  cold-blooded  vertebrates, 
adapted  to  life  in  the  water.  In  the  lower  forms  the  notochord 
persists  as  a  continuous  rod;  in  the  higher  fishes  it  is  replaced 
by  the  vertebra.  The  body  is  covered  with  a  skin,  in  which 
are  numerous  mucus-glands.  Scales  are  usually  present,  set 
in  pouches  in  the  skin.  In  the  great  majority  of  forms  gills  are 
the  only  organs  of  respiration.  Locomotion  is  usually  effected 
by  means  of  fins.  With  very  few  exceptions,  fishes  lay  eggs 
from  which  the  young  are  hatched ;  that  is,  they  are  oviparous. 

There  is  a  remarkable  uniformity  of  type  in  the  class  when 
the  number  of  species  (about  fifteen  thousand)  and  the  length 
of  time  they  have  been  in  existence  is  considered.  Professor 
Dean,  of  Columbia  University,  says  :  "  The  evolution  of  fishes 
has  been  confined  to  a  noteworthy  degree  within  rigid  and 
unshifting  bounds ;  their  living  medium,  with  its  mechan- 
ical effects  upon  fish  forms  and  structures,  has  for  ages  been 
almost  constant  in  its  conditions  ;  its  changes  of  temperature 
and  currents  have  rarely  been  more  than  of  local  impor- 
tance, and  have  influenced  but  little  the  survival  of  genera 
and  species  widely  distributed ;  its  changes,  moreover,  in  the 
normal  supply  of  food  organisms  cannot  be  looked  upon  as 
noteworthy." 

We  shall  consider  three  of  the  four  groups  into  which  the 
fishes  are  usually  divided. 

316 


THE  ALLIES  OF  THE   PERCH:   PISCES         317 

Sharks  and  Rays.  The  sharks  and  rays,  or  Elasmobran'chii 
(Gr.  elasmos,  plate ;  branchia,  gills),  are  fishes  with  a  cartilagi- 
nous skeleton  and  with  gills  which  communicate  with  the 
surface  by  several  openings,  instead  of  being  covered  by  an 
operculum,  as  in  the  perch.  The  skin  is  roughened  by  small 
tubercles,  which,  when  closely  set,  form  shagreen,  used  in 
the  arts  for  polishing  woods  and  for  ornamental  work.  The 
tail  is  usually  unequally  lobed,  the  dorsal  division  being  the 
larger. 

The  sharks  (Fig.  156)  are,  with  the  exception  of  one  species 
found  in  Lake  Nicaragua,  marine  animals,  and  are  developed 


FIG.  156.  Photograph  of  Shark.    (American  Museum  of  Natural  History) 

to  the  greatest  extent  in  the  tropics.  The  rays,  or  skates,  are 
more  flattened  forms,  adapted  to  a  life  on  the  bottom  of  the 
sea,  which  they  often  resemble  in  color.  Fig.  157  shows  a 
species  common  on  the  North  Atlantic  coast,  which  grows  to 
be  about  two  feet  in  length.  The  most  famous  of  the  rays 
are  the  torpedoes,  so  called  from  their  power  of  giving  an 
electric  shock.  About  fifteen  species  of  torpedoes  are  known, 
of  which  one  is  sometimes  found  on  the  eastern  coast  of  the 
United  States. 

Bony  Fishes.  The  bony  fishes,  or  Teleos'tomi  (Gr.  teleos,  com- 
plete or  perfect ;  stoma,  mouth),  in  the  higher  forms,  of  which 
the  perch  is  an  example,  have  the  skeleton  ossified  (converted 
into  bone)  and  the  body  usually  covered  with  scales ;  in  the 


318  GENERAL  ZOOLOGY 

lower  forms  the  body  may  be  covered  with  bony  plates,  and 
the  skeleton  may  be  hardly  more  ossified  than  in  the  group 
which  has  just  been  considered.  In  all  teleostomes,  however, 
the  gills  open  beneath  a  protecting  operculum.  The  order 
comprises  ninety-five  per  cent  of  all  known  fishes. 


FIG.  157.  Photograph  of  Skate 

The  garpikes  of  American  waters  illustrate  one  type  of 
body-covering,  consisting  of  bony,  enameled,  closely  set 
plates,  which  form  a  complete  coat  of  armor.  The  sturgeons 
(Fig.  158)  illustrate  another  type  in  which  the  armor  is 
greatly  reduced,  the  teeth  absent,  and  the  animals  adapted  to 
bottom-feeding  by  the  development  of  a  beak,  and  by  barbels 
for  feeling  for  their  food  in  the  mud.  Sturgeons  are  found  in 


THE  ALLIES  OF  THE  PERCH:   PISCES         319 

Europe  as  well  as  in  the  United  States  and  Canada.    One  of 
the  European  species  grows  to  be  over  twenty  feet  long. 

The  remaining  bony  fishes  have  fully  ossified  skeletons. 
The  eels  are  forms  in  which  the  body  is  greatly  elongated 
and  the  scales  reduced  to  almost  invisible  rudiments.  Loco- 
motion is  effected  by  snake-like  movements  of  the  body. 
The  common  eel  (Angml'la  chrys'ypa)  of  North  America  is 
found  along  the  Atlantic  coast  from  Newfoundland  to  Central 
America,  and  in  most  streams  and  ponds  in  the  eastern  states 


Fi<;.  158.  Photograph  of  Sturgeon 
(From  Jordan  and  Evermann's  American  Food  and  Game  Fishes) 

which  are  accessible  from  the  sea.  The  young  are  hatched 
on  mud-banks  in  the  Atlantic  Ocean,  often  near  the  mouth 
of  a  river.  The  eggs  are  laid  in  the  fall,  and  the  young,  at 
the  beginning  of  the  second  spring,  find  their  way  in  count- 
less numbers  up  the  various  streams,  where  they  complete 
their  development  and  return  to  the  sea  to  spawn.  After 
providing  for  the  new  generation  the  adult  eels  die,  never 
returning  to  fresh  water.  The  number  of  young  produced 
has  been  estimated,  in  the  case  of  an  eel  thirty-two  inches 
long,  to  be  10,700,000.  Eels  may  grow  to  be  four  feet  long. 


320 


GENERAL  ZOOLOGY 


The  Atlantic  salmon  (Sal1  mo  sa'lar)  is  a  well-known  food- 
fish  found  on  the  coasts  of  both  Europe  and  America.  Unlike 
the  eel,  the  salmon  spends  most  of  its  life  in  the  sea,  visiting 
the  fresh  water,  however,  to  spawn,  —  in  this  ascent  leaping 
waterfalls  which  may  be  in  its  way.  Leaps  of  over  twelve 
feet  have  been  recorded.  Several  allied  species  of  salmon 
are  extensively  canned  on  the  Pacific  coast. 

The  flatfishes  (including  among  other  fishes  the  flounders 
and  halibuts)  are  a  family  of  compressed  fishes,  dark  on  one 
side  and  light  on  the  other,  which  lie  on  the  light  side  on 


FIG.  159.  Flatfish 
(From  Report  of  Fur-Seal  Investigations) 

the  bottom  of  the  sea  (Fig.  159).  When  thus  placed  the 
dark  surface  is  protectively  colored  and  the  eyes  are  both  on 
the  upper  side,  which  is  sometimes  the  right  side  and  some- 
times the  left  side  of  the  body.  When  they  are  hatched  they 
have  an  eye  on  either  side  and  they  swim  like  other  fishes, 
though  with  a  slight  leaning  to  one  side,  which  becomes  more 
and  more  marked  as  they  develop,  till  they  finally  turn  entirely 
over.  The  eye  on  the  light  side  has  meanwhile  worked  its 
way  slowly  round  on  to  the  dark  side,  where  it  remains  with 
its  fellow,  looking  upward  when  the  fish  lies  on  the  bottom. 


THE  ALLIES  OF  THE   PERCH:   PISCES 


321 


The  absence  of  coloring  matter  on  the  side  which  is  in  con- 
tact with  the  bottom  seems  to  be  due  to  the  fact  that  little 
or  no  light  reaches  it,  for  when  a  number  of  young  floun- 
ders were  placed,  under  experimentation  by  Professor  Cun- 
ningham of  England,  so  that  the  under  side  was  illuminated 

by  a  mirror  for  four  months, 
nearly  all  the  specimens  devel- 
oped pigment  on  the  skin  of 
that  surface. 

The  sunfishes  are  interesting  on  account  of 
their  nest-building  habits.  They  scoop  out  a  space, 
sometimes  three  feet  across,  in  the  clear  sand  or 
gravel  in  shallow  water.  Here  the  eggs  are  laid, 
f  i^j  anc^  ^nen  guar(led  ty  both  parents,  their  pug- 
\  lit?  nacity  keeping  larger  fishes  at  a  distance. 

VlfL^5^  Lung-Fishes.  The  lung-fishes  (Fig.  160),  or 
Dip'noi  (Gr.  di,  two  ;  pneo,  breathe),  are  fishes 
with  an  almost  entirely  cartilaginous  skeleton, 
and  the  body  is  covered  with  scales  instead 
of  with  tubercles.  The  gills  are  covered  by  an 
operculum,  and  the  tail  tapers  to  a  point.  The 
structural  character  of  the  greatest  interest  is. 
suggested  in  their  common  name;  in  place  of 
the  air-bladder  there  is  a  true  lung,  or  pair 
of  lungs,  opening  from  the  ventral  side  of  the 
alimentary  canal.  Dipnoans  differ  from  other 

fisheS'  t0°'  in  the  fact  that  the  heart  is  incom" 
pletely  divided  into  three  chambers.    These  ani- 

mals are  interesting  as  the  possible  ancestors 
of  the  toads,  frogs,  and  their  allies,  which  we  shall  consider 
later.  Though  numerous  in  earlier  times,  there  are  but  three 
genera  now  in  existence,  one  each  in  the  rivers  of  Queens- 
land (in  Australia),  Brazil,  and  tropical  Africa.  "  The 
Australian  species  inhabits  rivers  which  at  certain  seasons 


Dean) 


Aftfr 


322  GENERAL  ZOOLOGY 

become  fetid  with  decaying  vegetation,  and  during  the  time 
it  breathes  air."  The  African  and  South  American  species 
"  bury  themselves  in  mud  during  the  dry  season,  a  necessary 
precaution,  since  they  inhabit  swamps  which  dry  up." 

Economic  Importance  of  Fishes.  The  value  to  a  people  of 
an  abundant  and  cheap  fish-supply  cannot  be  overestimated. 
Recognizing  its  importance,  the  United  States  government 
has  long  maintained  a  Commission  of  Fish  and  Fisheries 
(the  name  of  which  has  been  changed  recently  to  Bureau  of 
Fisheries),  which  has  been  active  along  both  practical  and 
scientific  lines.  Among  the  subjects  which  are  considered 
by  the  bureau  are  the  resources  of  our  inland  and  coastal 
waters,  the  geographical  distribution  of  the  economically  im- 
portant fishes  inhabiting  them,  and  the  study  of  the  natural 
history  of  fishes,  their  enemies,  diseases,  and  the  remedies 
therefor.  It  has  also  made  statistical  researches  into  the  con- 
dition and  commercial  value  of  the  fishing  industries  of  the 
United  States,  and  the  methods  employed  in  these  industries ; 
and,  perhaps  the  most  important  of  all,  it  has  carried  on  the 
artificial  propagation  and  distribution  of  valuable  species. 
Thus,  during  the  year  ending  June  30,  1901,  1,173,833,400 
fishes  and  eggs  were  distributed  to  different  parts  of  the 
United  States,  the  principal  species  being  shad,  salmon,  lake- 
trout,  whitefish,  pike,  perch,  lake-herring,  cod,  and  flatfish. 
In  this  way  many  bodies  of  water  have  been  restocked  after 
indiscriminate  destruction. 

Geographical  Distribution  of  Fishes.  A  simple  and  seem- 
ingly natural  classification  of  fishes,  as  regards  their  hab- 
itat, is  a  division  into  fresh-water  and  marine  forms  ;  and  this 
will  serve  our  purpose  if  it  be  remembered  that  there  has 
been  much  interchange  of  species  between  the  two  media. 
In  general,  the  truly  fresh-water  species  of  the  world  vary 
in  connection  with  the  great  faunal  regions  mentioned  on 
page  94.  In  the  North  American  and  Eurasian  realms  some 


THE  ALLIES  OF  THE  PERCH:   PISCES 


323 


important  fresh-water  families  are  the  sunfishes  (Centrar'chidce), 
the  perches  (Per'cidce),  and  the  catfishes  (Silur'idce).  Many  of 
the  salmon  and  trout  are  inhabitants  of  fresh  water,  though 
some  of  the  larger  species  are  marine,  visiting  fresh  water 
only  to  lay  their  eggs.  The  peculiar  distribution  of  the  few 
lung-fishes  which  have  survived  the  vicissitudes  of  geological 
time  has  already  been  mentioned.  When  allied  species  of 
animals  are  widely  scattered  over  the  globe  in  small  separated 
areas,  the  distribution 
is  spoken  of  as  dis- 
continuous. 

There  are  three 
common  divisions  of 
the  ocean  fauna,  - 
the  littoral  or  shore 
fauna,  the  pelagic  or 
open-sea  fauna,  and 
the  abysmal  or  deep- 
sea  fauna.  The  shore 
fishes  never  venture 
far  into  the  open  sea. 
Among  them  are  to 
be  included  the  large 

members  of  the  salmon  family  already  referred  to.  The  pelagic 
fishes  are  mostly  hunters  of  other  animals  in  the  sea  and  are 
strong  swimmers,  as  befits  their  environment.  Typical  fishes 
of  this  type  are  many  of  the  sharks. 

The  most  peculiar  forms  belong  to  the  deep-sea  fauna. 
There,  of  course,  the  conditions  are  unusual;  life  must  be 
adapted  to  an  enormous  pressure,  to  a  low  temperature  (not 
far  above  freezing),  and  to  absolute  darkness,  except  where 
it  is  lit  up  by  some  phosphorescent  animal.  Hence  the  fishes 
found  in  the  deep  waters  are  most  bizarre,  characterized  by 
uniformity  of  color-pattern,  often  black,  though  brighter 


FIG.  161.   Deep-Sea  Fish 
(From  Gunther's  Fishes) 


GENERAL  ZOOLOGY 

colors  are  sometimes  developed;  by  modifications  of  the 
eyes,  either  very  large  in  proportion  to  the  size  of  the  fish, 
or  entirely  absent;  by  the  development  of  tactile  and  phos- 
phorescent organs;  and  by  hypertrophy  (increase  of  size)  of 
mouth,  jaws,  and  stomach,  which  enables  the  fish  to  swallow 
an  animal  larger  than  itself.  Fig.  161  shows  one  of  these 
species. 

Geological  Development  of  Fishes.    We  left  the  geological 
history  of  the  development  of  animal  life  on  the  earth  at  the 


FIG.  162.   Devonian  Fishes 

end  of  the  Age  of  Invertebrates.  A  glance  at  the  map  on 
page  295  will  serve  to  recall  the  appearance  of  our  continent 
at  that  time.  In  North  America  the  Age  of  Invertebrates 
passed  slowly  and  quietly  into  the  Devonian  Period,  or  Age 
of  Fishes.  Though  numerous  kinds  of  invertebrates  already 
in  existence  rose  into  prominence,  or  passed  away  to  give 
place  to  new  forms,  the  chief  interest  centers  about  the 
fishes.  Geology  gives  us  no  hint  concerning  the  remote  an- 
cffctry  of  the  class.  The  earliest  fossil  fishes,  which  belong 


THE  ALLIES  OF  THE   PERCH:   PISCES         325 

to  the  latter  part  of  the  Age  of  Invertebrates,  are  represen- 
tatives of  the  sharks  and  rays,  lung-fishes,  and,  among  the 
bony  fishes,  forms  related  to  the  garpikes  of  to-day.  Thus 
all  the  great  groups  of  fishes  were  in  existence  very  early, 
with  the  single  exception  of  the  most  specialized  bony  fishes, 
of  which  the  perch  is  an  example.  Fig.  162  shows  two  spe- 
cies of  Devonian  fishes. 

The  earliest  fossil  remains  of  the  sharks  and  rays  are  frag- 
ments of  teeth  and  spines,  for  the  skeleton  was  not  fully 
ossified  and  no  coat  of  mail  was  developed.  The  shark-like 
forms  rose  to  great  prominence  in  the  course  of  the  Age 
of  Fishes,  a  little  later  becoming  the  predominant  type  of 
fishes,  of  which  our  species  to-day  are  but  the  scattered  rem- 
nants. The  sharks  are  especially  interesting  in  that  they 
probably  represent  most  nearly  the  ancestral  condition  of 
all  fishes,  and  hence  of  all  animals  with  a  back-bone.  The 
rays  are  more  modern  descendants  of  the  group,  adapted  to 
life  on  the  bottom. 

The  lung-fishes  were  also  a  dominant  group  very  early  in 
the  period.  By  the  end  of  the  next  succeeding  age  they  had 
practically  disappeared,  leaving,  as  has  been  noted,  but  few 
descendants  to-day.  Some  of  them,  which  have  been  found 
in  the  rocks  of  Ohio,  were  giants  among  fishes ;  they  were 
covered  with  great  plates,  at  least  anteriorly,  and  ranged  in 
length  from  ten  to  twenty-five  feet. 

Among  the  gar-forms  there  are  many  well-preserved  speci- 
mens, owing  to  the  fact  that  these  fishes  were  incased  in  a 
complete  coat  of  mail  formed  of  closely  interlocking  bony 
plates,  such  as  those  found  in  the  gaipike  and,  in  vestigial 
form,  in  the  sturgeon  of  to-day. 

The  other  bony  fishes,  forming  ninety-five  per  cent  of  all 
the  species  of  fishes  to-day,  may  well  be  called  modern  fishes, 
since  they  did  not  make  their  appearance  till  long  afterwards, 
in  the  Age  of  Reptiles. 


326  GENERAL  ZOOLOGY 

The  question  of  the  ancestry  of  the  fishes  is  one  of  the 
most  interesting  problems  of  zoology.  Though,  as  we  have 
seen,  geology  fails  to  answer  that  question,  and  probably 
never  will  be  able  to  answer  it,  on  account  of  the  presum- 
ably soft  character  of  the  ancestral  type ;  still,  by  considering 
what  has  been  learned  from  geology,  in  connection  with  the 
facts  of  embryology,  it  will  be  possible  to  trace  the  evolu- 
tion of  certain  organs. 
Thus  the  scales,  which 
form  so  characteristic 

a   covering  of  most 
FIG.  163.  Dermal  Fold  of  Fish.    (After  fighes    to.day?    can    be 

Wiedersheim)  .    . 

traced  to  their  origin 

in  limy  tubercles,  like  those  forming  the  shagreen  of  sharks. 
Teeth  originated  from  the  same  structures  along  the  margin 
of  the  mouth.  The  fins  are  looked  upon  by  some  ichthyol- 
ogists (students  of  fishes)  as  remnants  of  a  once  continuous 
fold  of  skin  (Fig.  163)  ;  others  regard  these  structures  as 
having  originated  from  external  gills,  or  from  modified  gill- 
arches.  Gills  first  arose  as  slits  in  the  wall  of  the  alimentary 
canal,  and  the  air-bladder  is  a  branch  of  the  same  structure. 

The  land  area  of  North  America  did  not  greatly  change 
throughout  the  Age  of  Fishes,  though  a  gradual  increase  in 
size  is  to  be  noted,  preparing  the  way  for  a  greater  develop- 
ment of  land  animals  and  plants,  to  which  reference  will  be 
made  after  some  study  of  the  frog  and  its  allies  in  the  follow- 
ing chapters. 


CHAPTER    XXV 
THE  GREEN  FROG 

Cardanus  undertakes  to  give  reason  for  the  raining  of  Frogs ;  but  if  it 
were  in  my  power,  it  should  rain  nothing  but  Water  Frogs,  for  those,  I  think, 
are  not  venomous.  —  IZAAK  WALTON,  The  Complete  Angler. 

Habitat  and  Distribution.  The  green  frog  (Ra'na  dam'itans) 
is  one  of  the  commonest  species  of  frogs  in  the  eastern  United 
States.  It  frequents  the  neighborhood  of  springs  and  meadow 


FIG.  164.  Photograph  of  Bullfrog.  Reduced 

brooks,  and  may  be  distinguished  from  its  larger  relative,  the 
bullfrog  (Rana  catesbia'na,  Fig.  164),  by  the  presence  of  two 
glandular  folds  of  skin  along  the  sides  of  the  back. 

External  Structure.    The  body  is  divisible  into  a  head  and 
trunk ;  there  is  no  visible  tail.    The  body-covering  is  a  soft, 

327 


328  GENERAL  ZOOLOGY 

smooth  skin  without  scales,  abundantly  supplied  with  mucus- 
glands.  There  are  four  appendages,  —  the  limbs,  the  anterior 
of  which  are  divisible  into  upper  arm,  forearm,  and  hand;  the 
posterior,  into  thigh,  lower  leg,  and  foot.  The  hand  ends  in 
four  short  fingers;  the  foot,  in  five  toes,  joined  by  a  web.  Both 
fingers  and  toes  are  often  spoken  of  as  digits.  The  eyes  are 
situated  prominently  on  the  top  of  the  head,  and  possess, 
in  addition  to  an  upper  eyelid,  a  thin  fold  of  skin  called 
the  nictitating  membrane,  which  can  be  drawn  across  the  eye- 
ball from  below.  There  is  no  true  lower  eyelid.  In  front  of 
the  eyes,  near  the  anterior  end  of  the  head,  are  the  external 
openings  of  the  nostrils;  posterior  to  the  eyes  are  smooth, 
round  spots,  the  tympanic  membranes,  the  outer  portions  of 
the  frog's  ears. 

The  Digestive  System.  The  wide  mouth-cavity  (Fig.  165, 1) 
narrows  into  the  short,  straight  oesophagus  (Fig.  165,  6). 
Conical  teeth  are  placed  along  the  edge  of  the  upper  jaw 
(Fig.  165,  2)  and  on  the  roof  of  the  mouth.  A  thick,  fleshy 
tongue  (Fig.  165,  3),  notched  posteriorly,  is  attached  by  its 
anterior  margin  to  the  ventral  surface  of  the  mouth-cavity. 
The  tongue  can  be  thrust  out  suddenly  for  quite  a  distance 
to  capture  food,  which  consists  largely  of  insects,  worms,  and 
mollusks.  Two  openings  lead  from  the  mouth  to  the  nostrils 
(Fig.  165,  4),  and  two  openings  (the  Eustachian  tubes,  Fig. 
165,  5)  communicate  with  the  ears.  The  stomach  (Fig.  165,  7) 
is  a  thick-walled  sac  tapering  gradually  into  the  coiled  small 
intestine  (Fig.  165,  8).  Beyond  the  small  intestine  the  ali- 
mentary canal  suddenly  increases  in  diameter,  forming  the 
large  intestine  or  rectum  (Fig.  165,  9),  which  passes  without 
change  of  diameter  into  the  terminal  cloaca  (Fig.  165,  10), 
communicating  with  the  surface  at  the  cloacal  opening  (Fig. 
165,  11).  Between  the  lobes  of  the  liver  (Fig.  165,  13)  lies  a 
large  gall-bladder  (Fig.  165,  14).  A  pancreas  (Fig.  165,  15) 
and  a  spleen  (Fig.  165,  16)  are  present. 


329 


330  GENERAL  ZOOLOGY 

The  Circulatory,  Respiratory,  and  Excretory  Systems.  The 
heart  inclosed  in  its  sac,  the  pericardium  (Fig.  165,  17),  has 
one  chamber  more  than  the  heart  of  the  perch,  by  the  divi- 
sion of  the  auricle  into  two  parts,  a  right  and  left  auricle 
(Fig.  165,  20,  18).  The  blood  is  aerated  in  the  lungs  (Fig.  165, 
25,  26),  the  walls  of  which  are  traversed  by  the  capillaries  of 
the  blood-system.  The  lungs  communicate  with  the  exterior 
by  means  of  the  windpipe  or  trachea  (Fig.  165,  24),  opening 
into  the  mouth  by  a  narrow  slit,  the  glottis  (Fig.  165,  23). 

Owing  to  the  additional  chamber  in  the  heart  and  the 
presence  of  lungs,  the  course  of  circulation  in  the  frog  is 
somewhat  different  from  that  in  the  perch.  The  aerated 
blood  returned  from  the  lungs  by  the  pulmonary  veins  is 
poured  into  the  left  auricle ;  the  non-aerated  blood  from  all 
over  the  body  is  returned  to  the  right  auricle.  The  auricles 
contract  at  the  same  instant,  forcing  both  venous  and  arterial 
blood  into  the  ventricle  (Fig.  165,  19),  which  in  turn  con- 
tracts before  there  has  been  much  mixing  of  the  two  kinds 
of  blood,  emptying  its  contents  into  the  arterial  circulation, 
the  beginnings  of  which  are  shown  in  Fig.  165,  21  and  22. 
As  the  arterial  system  takes  its  rise  from  the  right  side 
of  the  ventricle,  the  first  blood  to  enter  the  arteries  is  non- 
aerated.  Owing  to  the  less  pressure  in  the  arteries  which 
supply  the  lungs  and  skin,  and  the  presence  of  valves  which 
cut  the  blood  off  from  easily  entering  the  arteries  that  supply 
the  head  and  body,  most  of  the  non-aerated  blood  goes  to  the 
lungs  and  skin.  The  blood  which  follows  is  a  mixture  of 
aerated  and  non-aerated  blood,  and  the  pressure  being  raised 
by  the  presence  of  non-aerated'  blood  in  .the  capillaries  of  the 
lungs  and  skin,  this  blood  forces  the  valves  aside  and  makes 
its  way  to  the  different  parts  of  the  body,  except  the  head. 
In  the  course  of  the  artery  leading  to  the  head  is  a  structure 
(the  carotid  gland)  which  temporarily  obstructs  the  flow  of 
blood  till  the  body-arteries  have  become  filled  ;  and  the  supply 


THE  GREEN  FROG  331 

of  mixed  blood  having  become  exhausted,  the  head  receives 
only  aerated  blood.  The  impure  blood  from  the  organs  of  the 
body-cavity  and  from  the  hind  legs  returns  either  through 
the  liver  or  the  kidneys ;  while  that  from  the  head,  the  fore 
limbs,  and  from  the  skin  and  muscles  generally,  is  poured 
directly  into  the  right  auricle. 

The  frog  breathes  with  the  mouth  closed.  By  depressing 
the  tongue,  air  is  drawn  into  the  mouth-cavity  through  the 
nostrils.  When  the  tongue  is  raised  the  nostrils  close  by 
valves  and  the  air  is  forced  into  the  lungs.  Considerable 
exchange  of  gases  takes  place  through  the  soft,  moist  skin, 
which  is  well  supplied  with  blood-vessels  (Fig.  165,  28). 

The  lymphatic  system  is  well-developed  in  the  frog,  and 
the  lymph  is  assisted  in  its  circulation  by  two  pairs  of 
lymph-hearts,  one  at  the  posterior  end  of  the  body,  and  one 
in  the  region  of  the  shoulders.  The  pulsations  of  the  pos- 
terior lymphs-hearts  can  be  observed  externally  in  the  living 
frog. 

The  kidneys  (Fig.  165,  29)  are  a  pair  of  oval,  dark-red 
bodies  lying  in  the  dorsal  part  of  the  body-cavity.  The  ureters 
(Fig.  165,  30)  open  from  them  into  the  cloaca  (Fig.  165,  31). 
The  urinary  bladder  (Fig.  165,  32)  is  a  large,  thin-walled  sac 
projecting  ventrally  from  the  cloaca,  and  is  a  very  different 
organ  from  the  urinary  bladder  of  the  perch,  which  is  a  dila- 
tation of  the  ureter.  The  function  of  the  two  organs  is,  how- 
ever, the  same,  that  of  receiving  the  liquid  nitrogenous  waste 
from  the  kidneys. 

The  Skeletal  System.  In  general,  the  skeleton  of  the  frog 
is  built  upon  the  plan  seen  in  the  perch,  but  its  appendages 
are  considerably  more  specialized.  The  skull  (Fig.  166,  1) 
is  flattened  and  the  cranium  articulates  with  the  first  verte- 
bra by  two  surfaces,  or  condoles.  The  vertebral  column  consists 
of  nine  vertebrae,  terminated  by  a  long  bone  called  the  urostyle 
(tail-bone)  (Fig.  166,  3). 


3 


11 


FIG.  106.  Skeleton  of  Frog.    Natural  size.    (After  Duges) 

1,  skull;  2,  vertebral  column;  3,  urostyle;  4,  scapula;  5,  hmnerus;  6,  radius  and 
ulna;  7,  carpus;  8,  metacarpals ;  1),  phalanges  of  fore  leg;  10,  pelvic  girdle; 
11,  femur;  12,  tibia  and  fibula;  13,  tarsus;  14,  metatarsals ;  15,  phalanges  of 
hind  leg ;  16,  rudimentary  toe 


332 


THE  GREEN  FROG  333 

The  bones  of  the  arms  are  attached  to  a  shoulder-girdle 
consisting  of  the  shoulder-blades  or  scapulas  (Fig.  166,  4),  two 
coracoids,  and  two  collar-bones  or  clavicles.  A  broad  breast- 
bone (sternum)  extends  a  short  distance  along  the  median 
ventral  line.  Each  of  the  anterior  limbs  contains  one  bone  in 
the  upper  arm,  called  the  humerus  (Fig.  166,  5);  one  bone 
in  the  forearm,  composed  of  two  bones  united,  —  the  radius 
and  ulna  (Fig.  166,  6) ;  six  bones  in  the  wrist-region,  or  car- 
pus (Fig.  166,  7);  four  complete  sets  of  bones  in  the  palm 
(metacarpals,  Fig.  166,  8) ;  and  four  complete  sets  of  finger- 
bones  (phalanges,  Fig.  166,  9).  The  metacarpals  arid  phalanges 
of  the  inner  digit  are  rudimentary. 

The  leg-bones  are  attached  to  the  vertebral  column  by 
means  of  a  hip  01  pelvic  girdle  (Fig.  166,  10),  of  peculiar  shape. 
The  skeleton  of  each  leg  consists  of  one  bone  in  the  upper,  leg, 
the  femur  (Fig.  166,  11);  one  bone  in  the  lower  leg,  formed 
from  two  bones  united,  the  tibia  and  fibula  (Fig.  166,  12) ;  five 
bones  in  the  ankle-region,  or  tarsus  (Fig.  166,  13) ;  and  five 
complete  sets  of  phalanges  (Fig.  166,  15).  A  sixth  rudimen- 
tary digit  is  also  present  (Fig.  166,  16),  consisting  of  one 
metacarpal  bone  and  two  phalanges. 

The  Nervous  and  Muscular  Systems.  The  nervous  system 
is  similar  in  general  plan  to  that  of  the  perch.  The  brain  has 
large  cerebral  hemispheres  (cerebrum,  Fig.  165,  43),  each  of 
which  is  prolonged  anteriorly  into  an  olfactory  lobe  (Fig. 
165,  42).  The  optic  lobes  (Fig.  165,  44)  are  also  large,  but  the 
cerebellum  (Fig.  165,  45)  is  small.  Behind  the  cerebellum  is 
the  medulla  oUongata  (Fig.  165,  40),  at  the  posterior  end  of 
which  the  spinal  cord  (Fig.  165,  47)  arises.  The  nerves  are  not 
shown  in  the  dissection.  The  muscles  are  arranged  in  bands 
or  spindle-shaped  masses  instead  of  in  segments,  and  the  frog 
is  capable  of  much  more  complex  movements  than  the  perch. 

The  Reproductive  System.  The  spermaries  of  the  male 
frog  (Fig.  165,  49)  are  bean-shaped  bodies  lying  beneath  the 


334  GENERAL  ZOOLOGY 

kidneys,  to  which  they  are  attached.  The  ovaries  of  the  female 
frog  when  mature  fill  up  a  large  portion  of  the  body-cavity. 
Attached  to  the  anterior  end  of  the  spermaries  and  ovaries 
are  the  fat-bodies  (Fig.  165,  34),  —  lobed  organs  which  attain 
their  fullest  development  in  the  spring.  These  organs  are 
believed  to  be  of  use  as  storehouses  of  reserve  material,  ren- 
dering possible  the  formation  of  large  numbers  of  sperma- 
tozoa, or  eggs,  without  complete  exhaustion  of  the  animal. 
After  the  spawning  season  the  fat-bodies  decrease  in  size. 

Development.  The  eggs  of  frogs  (Fig.  167,  1,  2,  3)  are  laid 
early  in  the  spring  in  shallow  water  in  large,  jelly-like  masses. 
They  are  fertilized  by  the  male  as  they  leave  the  body  of  the 
female.  Within  a  week  or  ten  days  they  hatch,  the  time 
required  depending  largely  upon  the  temperature  of  the  water. 
At  first  the  young  is  blind,  and  is  without  gills  or  a  mouth;  it 
fastens  itself  to  weeds  and  other  objects  in  the  water  by  means 
of  a  crescent-shaped,  adhesive  apparatus  at  the  anterior  end 
(Fig.  167,  4).  Certain  areas  of  the  body  are  covered  with 
cilia,  by  the  vibration  of  which  the  animal  is  able,  even  with- 
out using  its  tail,  to  go  forward  in  the  water.  Eyes,  external 
gills,  and  a  mouth  provided  with  horny  jaws  soon  appear, 
and  the  young,  now  the  familiar  tadpole,  begins  to  feed  on 
plant  food  (Fig.  167,  5).  The -alimentary  canal  is  long  and 
coiled,  as  it  usually  is  in  animals  which  feed  upon  plant 
material.  The  heart  has  two  chambers. 

As  the  tadpole  increases  in  size  (Fig.  167,  6)  the  first  or 
primary  gills  are  replaced  by  secondary  gills,  which  soon  be- 
come covered  with  a  fold  of  skin,  the  operculum.  The  growth 
of  the  operculum  continues  till  the  gill-openings  are  covered, 
leaving  a  small  hole  usually  on  the  left  side.  In  this  fish-like 
condition  the  tadpole  continues  through  the  summer,  and  on 
the  approach  of  cold  weather  buries  itself  in  the  mud,  where 
it  hibernates.  In  some  species  of  frogs  the  tadpole  develops 
into  the  adult  form  in  the  course  of  a  single  season. 


FIG.  167.  Development  of  Frog 

1,  2,  3,  eggs;  4,  young  immediately  after  hatching;  5,  tadpole  with  external  gills 
6,  7,  8,  9,  10,  and  11,  further  stages  of  development;  12,  frog 

(From  Baskett's  Story  of  the  Amphibians  and  Reptiles) 
335 


336  GENERAL  ZOOLOGY 

If  the  adult  condition  has  not  been  reached,  the  tadpole 
continues  its  growth  the  following  summer.  The  hind  legs 
appear  (Fig.  167,  7,  8),  and  grow  to  be  about  an  inch  long, 
when  the  fore  legs  suddenly  appear  (Fig.  167,  9,  10).  The 
front  legs  are  really  formed  as  early  as  the  hind  legs,  but  they 
are  kept  beneath  the  skin  for  a  while.  The  broad  and  com- 
pressed tail,  which  forms  the  tadpole's  chief  organ  of  loco- 
motion, is  gradually  absorbed,  and  the  young  frog  finally  hops 
out  on  land  with  only  a  stump  of  a  tail  remaining  (Fig.  167, 11). 
By  the  time  these  changes  have  taken  place  externally,  im- 
portant changes  have  gone  on  inside  :  the  gills  have  been 
replaced  by  lungs ;  one  of  the  chambers  of  the  heart  has  been 
divided;  the  intestine  has  become  shorter,  fitting  the  frog 
better  for  an  animal-diet;  and  the  horny  jaws  have  given 
place  to  a  wide  mouth  with  teeth.  This  metamorphosis  is 
retarded  by  cold,  and  accelerated  by  rest  and  freedom  from 
disturbance  of  the  water.  The  frog  (Fig.  167,  12)  grows  for 
several  years  without  further  metamorphosis,  except  the 
gradual  disappearance  of  the  stump  of  the  tail.  Through- 
out life  the  outer  skin  is  cast  periodically  in  a  single  piece 
and  immediately  devoured. 

Relation  to  Environment.  The  dark-green  and  brown  colors 
of  the  upper  surface  afford  considerable  protection  among  the 
water-plants  and  along  the  muddy  or  grassy  margins  of  ponds 
and  streams,  and  the  white  under  surface  may  be  similarly 
useful  in  the  water. 

The  green  frog  is  a  voracious  feeder,  and  varies  its  diet 
with  almost  every  kind  of  small  creature  which  comes  its 
way,  not  hesitating  in  the  least  to  devour  smaller  individuals 
of  its  own  kind.  Usually  only  moving  objects  are  seized,  and 
it  has  been  said  that  the  frog  may  starve  to  death  in  the 
midst  of  an  abundance  of  food  if  there  is  no  movement  to 
attract  its  attention.  The  eyes  are  situated  high  on  the  top  of 
the  head,  where  they  maintain  a  wide  survey.  Every  boy  in 


THE  GREEN  FROG  337 

the  country  knows  of  the  difficulty  of  approaching  these  alert 
creatures,  and  he  knows,  too,  how  to  capture  them  by  dang- 
ling a  hook  with  a  piece  of  red  flannel  in  front  of  them. 
Even  if  well  fed  the  frog  seems  to  find  the  moving  object  irre- 
sistible, and  seizes  it  with  wide-open  mouth.  The  tongue  is 
covered  with  a  sticky  substance,  and  can  be  swiftly  extended 
with  unerring  aim  to  a  distance  of  several  inches. 

While  the  frog  depends  very  largely  on  the  sense  of  sight 
to  warn  it  of  approaching  enemies  or  enable  it  to  distin- 
guish food,  the  sense  of  hearing  is  also  of  considerable  value. 
Dr.  R.  M.  Yerkes,  of  Harvard  University,  who  has  studied 
the  sense  of  hearing  in  frogs  both  in  the  laboratory  and  in 
the  field,  says  that  he  is  convinced  that  sounds  which  are  of 
importance  in  the  life  of  the  animal,  as  the  splash  made  by 
a  frog  jumping  into  the  water,  are  not  only  heard,  but  that 
such  sounds  serve  to  put  other  frogs  on  their  guard.  The 
croaking  of  male  frogs  in  the  spring  is  undoubtedly  heard 
by  the  female,  and  serves  to  make  mating  more  certain. 

The  observer  just  quoted  does  not  give  the  green  frog 
credit  for  much  intelligence,  as  his  experiments  seem  to 
show  that  nearly  all  the  frog's  actions  are  repeated  with 
machine-like  accuracy,  and  new  habits  are  learned  very 
slowly.  He  is  inclined  to  think  that  even  the  perch  learns 
more  rapidly  than  the  frog.  He  also  notes  that  the  frog  is 
very  timid,  and  that  fright  tends  to  lengthen  the  process  of 
learning. 

When  suddenly  touched,  the  frog  may  do  one  of  several 
things:  it  may  jump,  using  the  strong  hind  legs  sometimes 
with  force  enough  to  carry  it  several  feet ;  it  may  remain 
perfectly  quiet ;  or  it  may  crouch  with  its  head  close  to 
the  ground,  at  the  same  time  puffing  itself  out.  This  last 
action,  Dr.  Yerkes  has  noticed,  more  often  takes  place  when 
the  animal  is  touched  in  front,  and  is  probably  useful  to 
render  seizure  difficult,  or  to  prevent  it  altogether.  If  the  frog 


338  GENERAL  ZOOLOGY 

leaps  away,  it  is  usually  into  the  water  with  a  loud  "plunk." 
A  few  swift  strokes  of  the  hind  legs  serve  to  carry  the  ani- 
mal to  shelter  beneath  protecting  debris  in  the  water.  There 
it  is  able  to  remain  for  a  considerable  period  without  the 
necessity  of  rising  to  the  surface  for  oxygen,  owing  to  the 
low  state  of  all  the  life-processes.  The  frog  has  numerous 
enemies,  among  which  are  owls,  hawks,  and  herons,  many 
snakes  and  other  reptiles,  and  several  fur-bearing  creatures 
which  come  to  the  water  in  search  of  food. 

During  the  winter  green  frogs,  like  some  other  frogs, 
hibernate  in  the  mud  at  the  bottom  of  pools.  With  return- 
ing spring  they  congregate  to  lay  their  eggs,  and  the  males 
may  then  be  heard  calling  to  the  females  in  an  unmusical 
uchung,"  "chung,"  which  is  not  as  familiar  a  sound,  per- 
haps, as  the  bass  voice  of  the  bullfrog  or  the  high-pitched, 
insistent  note  of  the  spring  "  peepers  "  (p.  344).  After  provid- 
ing for  the  reproduction  of  the  species,  the  green  frog  spends 
the  rest  of  the  summer  in  its  rather  solitary  life  on  the  bank 
of  some  stream  or  spring-hole. 


CHAPTER   XXVI 
THE  ALLIES  OF  THE  FROG :  AMPHIBIA 

Blue  dusk,  that  brings  the  dewy  hours, 
Brings  thee,  of  graceless  form  in  sooth 

Dark  stumbler  at  the  roots  of  flowers, 
Flaccid,  inert,  uncouth. 

EDGAR  FAWCETT,  A  Toad. 

Definition  of  Amphibia  (Gr.  amphibios,  capable  of  living  in 
both  air  and  water).  The  frog  belongs  to  the  class  Amphib'ia, 
to  which  belong  also  the  toads,  newts,  and  salamanders.  Am- 
phibians are  cold-blooded  vertebrates  covered  with  a  smooth 
or  rough,  moist  skin,  in  which  are  numerous  mucus-glands. 
In  the  immature  state  amphibians  are  adapted  to  a  life  in 
the  water,  and  breathe  by  gills ;  when  adult  the  gills  are  in 
the  majority  of  cases  absorbed,  and  the  animals  breathe  by 
lungs.  Four  limbs  are  usually  present.  Nearly  all  amphibians 
are  oviparous. 

Two  out  of  the  three  orders  into  which  the  class  is  divided 
will  be  discussed  here.  One  of  these  orders  includes  the  sal- 
amanders and  newts,  the  other  the  toads  and  frogs. 

Salamanders  and  Newts.  The  Urode'la  (Gr.  oura,  tail;  delos, 
conspicuous)  are  elongate  forms,  with  rounded  or  compressed 
tail.  They  are  often,  but  erroneously,  called  lizards,  and 
resemble  the  latter  only  in  external  form.  The  eggs  are  laid 
usually  in  the  water  in  strings,  or  in  large  masses  resembling 
frogs'  eggs,  or  singly,  attached  to  the  leaves  of  water-plants. 
Salamanders  and  newts  hatch  as  tadpoles,  which  develop  into 
the  adult  form  without  a  strongly  marked  metamorphosis.  The 
young  of  our  common  eastern  species  may  be  distinguished 
from  the  tadpoles  of  the  toad,  and  from  those  of  our  vari- 
ous species  of  frogs,  by  their  more  elongate  form,  and  by 


340 


GENERAL  ZOOLOGY 


the  presence,  usually,  of  two  short,  rod-like  organs,  called 
"  balancers,"  which  project  from  the  anterior  end  of  the  body 
near  the  mouth.  The  balancers  may  serve  as  sense-organs  of 
touch,  or  as  adhesive  disks,  in  addition  to 
the  use  suggested  by  their  name.  The  gills 
are  usually  visible  externally  for  a  longer 
period  than  is  the  case  with  the  toad  and 
the  frogs.  Some  species  retain  their  gills 
throughout  life,  though  the  lungs  are  also 
functional ;  in  others,  though  the  gills  are 
absorbed  in  adult  life,  the  gill-openings  are 
retained ;  in  still  others  all  traces  of  gills 
and  gill-slits  disappear;  and,  finally,  a  few 
species  lose  their  lungs  also,  when  mature, 
depending  entirely  upon  the  skin  for  res- 
piration. 

Of  the  five  species  which  retain  their  gills 
throughout  life,  three  are  found  in  the  sur- 
face-waters of  the  eastern  and  southeastern 
United  States,  and  one  in  the  subterranean  waters  of  Austria 
and  Texas  respectively.  Both  the  cave-inhabiting  species  live 
in  absolute  darkness,  far  below  the  surface  of  the  earth,  and 
are  colorless  and  blind.  The  white  skin  is  sensitive  to  light, 
and  has  been  changed  to  a  black  color  after  several  months  of 
exposure  under  ordinary  conditions.  Fig.  168  shows  the  Texan 
cave  salamander  (TypJdomoVge  rath'buni)  from  an  artesian  well 
one  hundred  and  eighty-one  feet  below  the  surface. 

The  genus  Amblydtoma  includes  some  of  the  largest  of 
our  species,  known  by  the  common  name  of  blunt-nosed  sal- 
amanders. The  color  is  black,  spotted  with  yellow.  As  these 
salamanders  are  protected  by  an  acrid  secretion  from  the 
mucus-glands  of  the  skin,  the  conspicuous  colors  are  possi- 
bly to  be  interpreted  as  warning  coloration.  The  adults  live 
in  damp  places  and  lay  eggs  in  the  water  in  large  masses 


FIG.  168.  Cave  Sala- 
mander. Slightly 
Reduced.  (After 
Eigenmann) 


THE  ALLIES  OF  THE  FROG:   AMPHIBIA        341 

resembling  frogs'  eggs,  though  the  jelly-like  mass  which  sur- 
rounds them  is  more  opaque.  The  young  keep  their  gills  for 
a  considerable  period,  and  one  species,  called  the  axolotl 
(Amblystoma  tigri'num,  Fig.  169),  found  from  New  York  to 
California  and  Mexico,  may  even  breed  in  the  gill-bearing 
larval  stage.  These  immature  forms  live  in  the  water,  grow- 
ing to  be  eight  or  nine  inches  long,  or,  in  exceptional  cases, 
even  larger,  and  may  continue  in  this  condition  for  years,  with- 
out ever  changing  to  the  adult  form.  An  observer  who  has 


FIG.  169.  Photograph  of  Young  Axolotl.   Reduced.    (By  H.  V.  Letkemann) 

had  opportunity  to  study  axolotls  in  their  native  habitat  says 
that  the  change  to  the  adult  condition  is  hastened  by  abun- 
dance of  food,  and  by  the  partial  drying  up  of  the  water  and 
consequent  increase  in  temperature  of  the  water  which  remains. 
Like  some  other  amphibians  these  salamanders  can  regen- 
erate lost  limbs.  This,  according  to  Professor  Gadow,  of  Cam- 
bridge, England,  takes  place  more  certainly  and  quickly  the 
younger  the  animal  is.  In  one  case  quoted  by  this  authority 


342 


GENERAL  ZOOLOGY 


the  hand  of  an  axolotl  ten  years  old  was  removed,  and  it 
was  replaced  within  twelve  weeks.  Often  more  than  the 
usual  number  of  digits  is  replaced ;  this  tendency  is  greatest 
in  those  cases  where  the  limb  is  cut  off  close  to  the  body. 

The  Alpine  salamander  (Salaman'dra  a'tra),  found  in  moist 
places  two  thousand  feet  in  altitude,  especially  near  water- 
falls, in  the  Alps  of  Europe,  is  remarkable  for  its  breeding- 
habits.  Only  two  young  are  produced  at  a  time,  and  these 
are  born  alive  at  an  advanced  stage  of  development.  During 


FIG.  170.  Development  of  Newt.    Reduced.    (After  Gage) 

A,  Egg  on  water-plant;  Ji,  larva  (in  August);  C,  young,  in  autumn;  D,  about 
two  years  old ;  E,  adult 

the  time  they  are  within  the  mother's  body  they  are  nour- 
ished by  the  nutritive  matter  from  several  eggs,  which  only 
partially  develop. 

The  newts,  or  tritons,  are  carnivorous  salamanders  which 
are  more  or  less  aquatic  in  their  habits  when  adult,  or,  at 
least,  during  the  breeding-season,  at  which  time  also  the  colors 
of  the  males  in  some  species  become  brighter,  and  a  crest  is 
developed  along  the  back.  The  common  species  of  the  eastern 
United  States  (Diemy c' tylus  virides' cens,  Fig.  170)  is  olive- 
green  or  reddish  in  color,  with  a  compressed  tail  and  a  row  of 
small  orange-colored  spots  along  the  right  and  left  sides  of 
the  body.  It  grows  to  the  length  of  three  and  a  half  inches. 
The  eggs  (Fig.  170,  A)  are  laid  during  April,  May,  or  June, 
usually  in  the  axils  of  leaves  of  water-plants,  and  the  leaves 
are  drawn  together  and  made  into  a  compact  mass  by  a 


THE  ALLIES  OF  THE  FROG:  AMPHIBIA       343 

secretion  from  the  oviduct.  As  a  general  rule  one  egg  is  laid  at 
a  time  ;  occasionally  two  are  inclosed  in  the  same  mass.  The 
young  hatch  in  from  twenty  to  thirty-five  days,  depending 
on  the  temperature.  In  August  they  resemble  Fig.  170,  B. 
Late  in  the  fall  they  leave  the  water  and  live  on  land  in 
damp  places  beneath  logs  and  leaves  in  the  woods.  They 
are  then  of  a  beautiful  red  color  and  have  a  cylindrical  tail 
(Fig.  170,  C).  Several  years  are  required  to  produce  the 
aquatic  adult  form  (Fig.  170,  E). 

Toads  and  Frogs.  The  members  of  the  order  Anu'ra  (Gr.  an, 
without;  oura,  tail)  undergo  a  well-marked  metamorphosis. 
They  are  tadpoles  at  first,  and  later  change  to  the  adult 
condition  by  the  absorption  of  the  tail  and  the  development 
of  legs. 

Many  examples  of  peculiar  breeding-habits  are  known. 
The  female  of  a  Brazilian  species  of  tree-frog  (Hy'la  fa'ber) 
lays  her  eggs  within  a  circular  wall  of  mud  which  she  con- 
structs on  the  bottom  of  a  shallow  pool  of  water.  Within 
this  nursery  the  tadpoles  develop,  unless  liberated  by  the 
rain  or  other  accident.  Several  species  lay  their  eggs  on  the 
leaves  of  trees  above  the  water,  into  which  the  young  fall 
when  hatched.  The  male  of  the  obstetrical  toad  of  Europe 
(Al'ytes  obstet'ricus)  winds  the  eggs  around  his  legs,  and,  seek- 
ing a  safe  place,  guards  them  till  they  hatch.  In  a  South 
American  species,  the  famous  Surinam  toad  (Pi1  pa  ameri- 
ca'na),  the  eggs  are  spread  by  the  male  over  the  back  of  the 
female,  where  each  egg  becomes  covered  with  a  growth  of 
skin,  forming  a  pouch  with  a  lid.  Here  development  goes 
on,  and  the  entire  metamorphosis  takes  place  within  the 
egg.  In  a  Chilian  species  (Rhinoder'ma  Darwin'ii)  the  eggs 
are  transferred  by  the  male  to  vocal  sacs  at  the  side  of  the 
mouth,  which  become  greatly  developed  at  the  breeding- 
season.  Metamorphosis  takes  place  within  these  sacs,  and 
the  young  escape  in  the  adult  condition.  In  half  a  dozen 


344 


GENERAL  ZOOLOGY 


species  of  tree-frogs  from  South  America  (Nototre'ma)  the 
females  possess  dorsal  pouches  in  which  the  eggs  are  placed. 
The  young  appear  either  as  tadpoles  or  as  perfect  frogs. 

The  tree-frogs  or  tree-toads  are  forms  adapted  to  an  arbo- 
real existence.  They  possess  soft  pads  on  the  end  of  the 

digits.  Many  of 
them,  like  our 
common  tree-toad 
(Hyla  versic'olor, 
Fig.  171),  are  pro- 
tectively colored, 
and  have  the 
power  of  chan- 
ging their  color 
through  various 
shades  of  gray  and 
green.  A  South 
American  species 
is  conspicuously 
marked  with  red 
and  blue.  Experi- 
ments seem  to 
show  that  it  is  so 
well  protected  by 
an  acrid  secretion 
that  it  is  not  fed 

upon  by  birds,  which  might  otherwise  devour  it.  Several  of 
our  smaller  species  of  tree-toads,  called  "  peepers "  in  the 
country,  give  utterance  to  shrill  notes,  which  are  among  the 
first  sounds  of  spring.  In  that  season  they  seek  the  ponds  to 
mate  and  lay  their  eggs. 

The  common  toad  (Bu'fo  lentigino'sus)  is  one  of  the  farmers' 
most  valuable  allies  in  the  destruction  of  injurious  insects. 
Despite  the  prejudice  which  its  appearance  still  excites  among 


Fi<;.  171.   Photograph  of  Tree-Frog.     Reduced 


THE  ALLIES  OF  THE  FROG:  AMPHIBIA        345 

those  who  do  not  understand  it,  the  animal  is  a  most  inter- 
esting object  for  study.  There  is  no  truth  in  the  oft-repeated 
statements  of  its  poisonous  qualities,  except  in  so  far  as  the 
acrid  secretion  of  the  skin,  which  is  a  protection  to  many 
amphibians,  might  be  injurious  if  it  gets  on  sensitive  sur- 
faces, such  as  the  lining  of  the  eyelids.  The  dark-colored 
eggs  are  laid  in  long  strings,  like  a  string  of  beads,  in  shal- 
low water,  usually  in  April,  in  the  latitude  of  New  York. 
They  hatch  in  two  or  three  weeks  into  small  black  tadpoles, 
which  pass  through  their  transformation  within  about  two 
months. 

Geological  Development  of  Amphibians.  As  time  passed  on 
from  the  Age  of  Fishes  a  large  portion  of  the  great  interior 
sea  of  North  America,  shown  on  the  map,  page  295,  became 
a  region  of  swamps,  though  many  times  depressed  and  exposed 
to  the  inroads  of  the  sea.  These  conditions  brought  about  the 
formation  of  the  great  coal-beds  of  the  continent,  alternating 
with  beds  of  shale,  sandstone,  and  clay.  When  the  land  was 
above  the  surface  of  the 
water,  vegetation  flour- 
ished in  more  than  tropi- 
cal luxuriance ;  when  the 
land  was  depressed,  the 

ocean-waters    rolled    in 

FIG.  172.   Skull  of  Labyrmthodont 

and  destroyed  the  life  of 

the  land.  The  swamps  of  that  time  are  the  coal-beds  of 
to-day,  and  the  period  is  known  as  the  Carboniferous  Age 
or  Age  of  Coal  Plants.  Though  fishes  and  many  invertebrate 
forms  were  abundant,  progress  had  been  made  over  pre- 
ceding periods  in  the  development  of  back-boned  creatures 
adapted  to  breathing  air.  These  were  amphibians,  and  from 
the  prevalence  of  species  of  this  order  the  period  is  often  called 
the  Age  of  Amphibians.  There  were  snake-like  forms  without 
limbs,  and  forms  with  every  degree  of  limb-development. 


346 


GENERAL  ZOOLOGY 


Some  species  grew  to  be  as  large  as  alligators.  Their  skulls 
(Fig.  172)  were  solidly  roofed  over  with  bone.  Their  teeth, 
in  many  cases,  showed  complicated  foldings  of  the  enamel ; 
hence  they  have  been  called  labyrinthodonts,  i.e.  labyrinth- 
toothed  (Fig.  173).  There  is  little  doubt  that  the  labyrinth- 
odonts descended  from  the  fishes.  Anurans  and  urodeles  did 
not  appear  till  later.  Both  are  probably  descended  from  the 
labyrinthodonts,  each  by  its  own  line  of  ancestry. 

The  close  of  the 
Age  of  Amphibi- 
ans is  marked  by  a 
great  change  in  the 
topography  of  North 
America,  for  it  was 


Appalachian  system 
of  mountain  ranges 
was  uplifted.  This 
brought  a  great  area 
of  land  in  eastern 
North  America  above 
FIG.  173.  Section  of  Tooth  of  Labyrinthodont  ^e  level  of  the  sea, 

(From  Baskett's  Story  of  the  Amphibians  and     as    jg    shown    on    the 
Reptiles)  .  _  .  x        ^T 

map  (Fig.  174).    No 

species  of  animal  of  earlier  time  is  known  to  have  existed 
after  this  upheaval.  The  causes  underlying  the  culmination 
and  decline  of  so  many  species  at  this  time  are  not  thor- 
oughly understood.  They  are  probably  connected  with  the 
changes  already  spoken  of,  with  the  decline  in  the  temper- 
ature, and  with  the  slow  removal  of  carbon  dioxide  from 
the  atmosphere. 

Paleozoic  Time :  Era  of  the  Ancient  Forms  of  Life.  The 
geological  periods  so  far  considered  since  the  close  of  Archrean 
Time  (see  pp.  295,  324,  and  345)  are  usually  grouped  under 


THE  ALLIES  OF  THE  FROG:  AMPHIBIA       347 


the  general  heading  of  Paleozoic  Time,  or  the  Era  of  the 
Ancient  Forms  of  Life.  The  paleozoic  invertebrate  world 
was  peculiar  in  its  corals,  crinoids  (p.  246),  trilobites  (p.  153), 
brachiopods  (p.  233),  mollusks  of  the  orthoceras-type  (p.  193), 
and  in  its  insects,  which  were  largely  of  those  groups  which 
develop  without  metamorphosis.  Among  the  vertebrates, 
the  fishes  represented  were  sharks  and  rays,  gar-forms  and 


FIG.  174.  North  America  after  the  Appalachian  Revolution 
(From  Dana's  Manual  of  Geology) 

lung-fishes.  The  Appalachian  revolution  wiped  the  trilobites 
entirely  out  of  existence ;  the  corals  and  orthoceras-forms 
disappeared  soon  after,  with  but?  few  exceptions ;  the  brachio- 
pods were  much  diminished  in  numbers  ;  and  the  insects 
which  developed  without  strongly  marked  metamorphosis 
after  hatching  dwindled  away  before  the  rapid  rise  of  forms 
which  underwent  a  complete  metamorphosis.  The  sharks, 
rays,  gars,  and  lung-fishes  of  the  era  became  extinct  as  the 
higher  bony  fishes  began  to  people  the  sea. 


CHAPTER  XXVII 
THE  PINE-LIZARD  AND  ITS  ALLIES  :  REPTILIA 

I  only  know  thee  humble,  bold, 
Haughty,  with  miseries  untold, 
And  the  old  curse  that  left  thee  cold, 
And  drove  thee  ever  to  the  sun 
On  blistering  rocks. 

BRET  HARTE,  The  Rattlesnake. 

THE    PlNE-LlZARD 

Habitat  and  Distribution.  The  pine-lizard  (Scelop'orus  un- 
dula'tus,  Fig.  175),  or  swift  as  it  is  often  called,  is  found  in 
the  eastern  United  States  as  far  north  as  Michigan,  prefer- 
ring the  more  sandy  areas  covered  with  pine.  It  is  a  graceful 
little  creature  about  seven  inches  long,  gray  in  color  above, 
with  faint  undulating  black  stripes,  and  silvery  white  below. 
The  male  is  ornamented  with  lustrous  patches  of  blue  or 
green,  edged  with  black  on  the  sides  of  the  throat  and  under 
surface  of  the  body.  Old  fences  which  border  pine-lands  are 
favorite  resorts,  and  here  it  pursues  and  captures  countless 
insects.  Like  others  of  its  kind  this  lizard  loves  the  sun,  and 
is  to  be  found  active  only  in  the  hottest  part  of  the  day. 
During  the  cold  weather  it  hibernates,  at  least  in  the  northern 
part  of  its  range. 

External  Structure.  The  body  is  elongate  in  form,  resem- 
bling that  of  the  salamanders,  but  the  skin  is  covered  with 
scales  instead  of  being  smooth,  and  there  are  no  mucus-glands. 
The  digits  of  the  four  legs  are  long  and  slender,  and  have 
sharp  claws,  which  are  admirably  fitted  for  clinging  to  in- 
equalities in  the  bark  of  trees.  The  gray  color  of  the  back  is 
protective  when  the  lizard  is  at  rest,  and  its  movements  are 

348 


PINE-LIZARD  AND  ITS  ALLIES:    REPTILIA      349 

so  quick  that  it  is  difficult  for  the  eye  to  follow  them.  When 
alarmed  the  scales  can  be  raised,  the  throat  patches  swollen, 
and  the  head  elevated.  The  harmless  little  creature  then 
looks  quite  formidable.  In  order  to  provide  for  growth  the 
scaly  skin  is  cast  periodically. 

Internal  Structure.    The  internal  structure  is,  in  general, 
similar  to  that  of  the  amphibians,  but  in  several  respects  it 


FIG.  175.  Pine-Lizard.    Reduced 

indicates  a  higher  type  of  animal.  Thus,  the  lizard 
breathes  by  lungs  at  all  periods  of  its  life.  The 
heart  has  a  longitudinal  partition  extending  par- 
tially through  the  posterior  chamber  (Fig.  176,  19), 
so  that  there  is  an  incomplete  separation  into  right 
and  left  ventricles.  As  in  the  frog,  the  left  auricle  (Fig.  176, 18) 
receives  aerated  blood  returned  from  the  lungs  (Fig.  176,  30) 
by  the  pulmonary  veins  (Fig.  176,  24)  and  the  right  auricle 
receives  the  blood  from  the  rest  of  the  body  (Fig.  176,  25). 
From  the  right  side  of  the  ventricle  arises  the  pulmonary 
artery  (Fig.  176,  23) ;  from  the  left  side  are  given  off  the 
branches  of  the  artery  supplying  the  head  and  body  generally 
(Fig.  176,  20,  21,  22).  When  both  auricles  contract,  the  venous 
blood  in  the  right  auricle  tends  to  keep  to  that  side  of  the 
heart,  and,  by  the  aid  of  the  incomplete  partition,  is  forced 
into  the  pulmonary  artery;  the  arterial  blood  from  the  left 


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350 


PINE-LIZARD  AND  ITS  ALLIES:    REPTILIA     351 

auricle,  with  some  admixture  of  venous  blood,  is  driven  to 
the  arterial  branches  supplying  the  head  and  body  generally. 
The  nervous  system,  especially  the  brain,  is  also  more  highly 
differentiated  than  in  the  amphibians,  and  the  bones  are  more 
completely  ossified.  A  skeletal  difference  is  the  articulation 
of  the  cranium  to  the  first  vertebra  by  means  of  a  single  con- 
dyle.  A  study  of  Fig.  176  will  make  clear  the  relation  of  the 
most  important  organs. 

Development.  The  female  pine-lizard  lays  her  eggs  in  the 
ground,  a  short  distance  below  the  surface ;  ten  or  fifteen 
eggs  are  deposited  in  each  lot.  The  eggs  are  oblong  in  shape, 
from  fourteen  to  eighteen  millimeters  (a  little  over  half  an 
inch)  in  length,  and  are  roughened  on  the  surface,  causing 
dirt  to  adhere  to  them.  One  lot  brought  to  an  observer  in 
North  Carolina  late  in  the  month  of  June  had  been  plowed 
up.  The  eggs  increased  in  size  as  the  embryo  developed, 
finally  hatching  in  about  two  months.  The  young  resemble 
the  adult  quite  closely  in  everything  but  size.  They  are  able 
to  take  care  of  themselves  from  the  first. 


THE  ALLIES  OF  THE  PINE-LIZARD:  REPTILIA 

Definition  of  Reptilia.  The  pine-lizard  will  serve  as  an 
example  of  the  class  Reptil'ia  (Lat.  repere,  to  creep),  which 
includes  also  snakes,  turtles,  tortoises,  alligators,  and  croco- 
diles. Reptiles  are  cold-blooded  vertebrates  covered  with 
scales  or  plates  ;  they  breathe  by  lungs  throughout  their  life. 
A  few  reptiles  are  viviparous,  but  most  of  them  lay  eggs, 
from  which  the  young  hatch  in  the  form  of  the  adult. 

Four  out  of  the  five  groups  into  which  the  class  may  be 
divided,  are  here  considered. 

Lizards.  Most  of  the  Lacertil'ia  (Lat.  lacerta,  a  lizard)  are, 
like  the  pine-lizard,  elongate  reptiles  with  four  limbs  and 
movable  eyelids.  A  few  families  have,  however,  lost  one  or 


352 


GENERAL  ZOOLOGY 


both  pairs  of  limbs  in  connection  with  their  adoption  of  a 
burrowing  life,  and  the  eyes  have  disappeared  beneath  the 


FIG.  177.   Photograph  of  Legless  Lizard 

skin.    The  covering  of  scales,  so  characteristic  of  reptiles,  has 
also  in  some  cases  become  much  reduced.     Legless  lizards 


FIG.  178.  Photograph  of  Mexican  Iguana 

(Fig.  177)  may  be  distinguished  from  the  snakes,  which  they 
resemble,  by  the  fact  that  they  are  incapable  of  opening  the 
mouth  to  so  great  an  extent  as  snakes  are. 


PINE-LIZARD  AND   ITS  ALLIES:    REPTILIA     353 

Many  lizards  possess  the  power,  when  seized  suddenly,  of 
snapping  off  the  tail,  which  may  be  left  in  possession  of  the 
captor,  while  the  creature  hurries  away  to  safety.  Fig.  179 
shows  a  Mexican  species  of  iguana  which  had  thus  responded 
to  the  efforts  of  the  photographer  to  take  its  picture.  The  same 
animal  before  mutilation  is  shown  in  Fig,  178.  The  .tail  is 
usually  reproduced,  at  least  so  far  as  the  flesh  and  skin  are 


FIG.  179.  Photograph  of  Mexican  Iguana  with  Broken  Tail 

concerned ;  new  vertebrae  are  not  developed.  The  pattern 
of  the  scales  on  the  newer  portion  is  usually  simpler,  some- 
times apparently  reverting  to  an  ancestral  type. 

The  chameleons  (Chame'leo)  of  the  Old  World  are  famous 
for  their  color  changes,  but  the  power  is  possessed  to  a  greater 
or  less  extent  by  nearly  all  lizards.  It  is  accomplished  by  the 
shifting  of  pigment  granules  in  cells  in  the  deeper  layers  of 
the  skin,  toward  or  away  from  the  colorless  outer  skin.  The 
movement  of  the  granules,  though  affected  by  external  con- 
ditions, such  as  color  and  temperature  of  surrounding  objects, 
is  said  to  be  largely  under  the  control  of  the  animal. 

Snakes.  The  snakes,  which  belong  to  the  class  Ophid'ia 
(Gr.  ophis,  a  serpent),  are  usually  very  easily  distinguished 


354 


GENERAL  ZOOLOGY 


—  13 


externally  by  the  absence  of  eyelids  and  limbs,  although 
rudimentary  hind  legs  are  to  be  found  in  a  few  forms,  such 
as  the  pythons  of  Asia,  Africa,  and  Australia.  Teeth  are 

present  in  all  ophidians, 

...^^y;^ ^  •*- 

and  are  of  two  types,  — 
the  ordinary  teeth,  used 
for  seizing  food,  and  the 
poison-fangs,  which  are 
perforated,  forming  a 
passage  for  the  poison 
secreted  in  a  gland  at 
their  base.  Both  kinds 
of  teeth  are  shown  in  the 
illustration  of  the  skull 
of  the  rattlesnake  (Fig. 
180),  which  shows  also  the 
gland  where  the  poison  is 
secreted  (Fig.  180,  9),  and 
the  reserve  fangs  (Fig. 
180, 11)  which  replace  the 
first  pair  when  the  former 
are  broken  or  shed.  In  the 
non-poisonous  species  the 
number  of  teeth  is  much 
greater  than  in  the  rattle- 
snake. 

The  tongue  of  a  snake 
is  a  long,  slender,  forked 
structure,  used  principally 
as  an  organ  of  touch.  The 
lower  jaw  is  joined  to  the  upper  jaw  in  such  a  way  (see  Fig. 
180)  as  to  admit  of  so  much  freedom  of  movement  that  the 
snake's  mouth  can  be  opened  wide  enough  to  swallow  animals 
greater  in  diameter  than  itself.  The  passage  of  food  into  the 


Fir..  180.    Skull  of  Rattlesnake,  showing 
Poison-Fangs 

1,  2,  bones  of  cranium;  3,  prefrontal  bone; 
4,  quadrate  bone;  5,  maxillary  bone; 
6,  fang ;  7,  bones  of  lower  jaw ;  8,  tip  of 
snout ;  9,  poison-gland  ;  10,  poison-duct ; 
11,  reserve  fangs ;  12,  tip  of  fang ;  13,  tem- 
poral muscle 

(From  Baskett's   Story  of  the  Amphibians 
and  Reptiles) 


PINE-LIZARD  AND  ITS  ALLIES:    REPTILIA     355 


oesophagus  is  facilitated  by  an  abundant  secretion  from  sali- 
vary glands,  and  escape  of  the  prey  is  prevented  by  the  sharp, 
backward-pointing  teeth  in  both  jaws.  The  union  of  the  two 
sides  of  the  lower  jaw  in  front  is  so  loosely  made  by  a  carti- 
laginous connection  that  each  side  of  the  jaw  can  be  pushed 
forward  independently,  thus  getting  a  fresh  hold  on  the  food- 
mass.  Some  of  the  larger  snakes,  as  the  pythons  and  boas, 
kill  their  prey  by  constriction ;  the  non-poisonous  kinds  may 
swallow  theirs  alive  ;  the  poisonous  species  generally  kill  the 
animal,  unless  it  be  a  small  one.  Snakes  progress  by  means 
of  muscles  attached  to  the  ribs  and  scales  of  the  under  side. 
These  scales  have  a  free  posterior  edge,  which  can  be  inserted 
into  rough  places  in  the  surface  of  the  ground. 

The  poisonous  snakes  of  the  United  States  are  the  prettily 
colored  beadsnake  (E'laps  ful'vius)  and  the  water-moccasin 
(Agkis'trodon 
pisciv'orus)  of 
the  southern 
states  ;  the 
copperhead 
(Agkistrodon 
contor'trix], 
found  from 
New  England 
to  Wisconsin 
and  southward; 
and  more  than 
a  dozen  species 
of  rattlesnakes 


FIG.  181.  Photograph  of  .Rattlesnake 


(Fig.  181),  found  mostly  in  the  arid  regions  of  the  West 
and  Southwest.  The  use  of  the  peculiar  horny  appendage 
at  the  end  of  the  tail  of  the  rattlesnake  has  occasioned 
much  discussion.  By  some  it  has  been  thought  to  be  a 
means  of  terrifying  its  prey,  so  that  escape  may  be  rendered 


356 


GENERAL  ZOOLOGY 


impossible  ;  by  others  it  has  been  regarded  as  a  sex-call  for 
its  mate,  or  even  as  a  lure  for  birds.  Many  naturalists  con- 
sider that  its  function  is  similar  to  that  of  the  yellow  and 
black  coloration  of  wasps,  or  the  distinctive  red  markings  of 
poisonous  spiders,  —  features  which  serve  to  mark  the  pos- 
sessor as  having  unusual  means  of  defense.  By  the  mere 


FIG.  182.  Photograph  of  Blacksnakes 

fact  of  this  advertisement  it  is  thought  many  conflicts  are 
avoided  which  might  prove  disastrous  to  the  rattlesnake, 
even  if  the  attacker  were  killed  in  the  contest.  As  it  is, 
an  animal  must  have  some  confidence  in  its  powers,  if  it 
disregards  the  warning  rattle  and  tries  conclusions  with 
the  owner.  A  diamond-back  rattlesnake  in  captivity  in  the 
New  York  Zoological  Park  grew  a  new  "button"  to  the 
rattle  every  three  months,  on  each  occasion  of  shedding 
its  skin. 


PINE-LIZARD  AND  ITS  ALLIES:    REPTILIA     357 

Of  the  non-poisonous  snakes  of.  this  country  the  little 
green  snake  (Cy'elophis  verna'lis)  is  one  of  the 'most  interest- 
ing and  beautiful.  When  kept  in  confinement  it  is  a  harmless 
and  interesting  pet.  As  much  cannot  be  said  for  our  water- 
snakes  (Tropidono'tus),  which  are  of  irritable  disposition  and 
disposed  to  strike  when  handled.  Blacksnakes  (Basca'nion, 
Fig.  182)  have  been  kept  in  captivity  and  handled  freely  after 
they  have  become  accustomed  to  their  new  surroundings. 

Turtles  and  Tortoises.  The  turtles  and  tortoises,  Chelo'nia 
(Gr.  chelone,  a  tortoise),  are  externally  the  best  protected  of 
all  the  reptiles,  being  incased  in  a  shell  formed  of  plates 
firmly  fixed  to  the  vertebrae  and  ribs.  Chelonians  have  no 
teeth,  but  the  rim  of  the  jaws  is  covered  with  a  horny  skin. 
The  limbs  are  sometimes  modified  into  flippers  for  locomo- 
tion in  the  water  ;  to  such  species  the  name  "  turtle  "  is  com- 
monly applied.  The  tortoises  are  land  and  fresh-water  species, 
with  claws  on  the  digits. 

Of  the  turtles,  the  green  turtle  (Ohelo'ne  my' das)  of  the 
warmer  portion  of  the  Atlantic,  Indian,  and  Pacific  oceans, 
and  the  hawkbill  (Ohelone  imbrica'ta),  also  widely  distributed 
in  warm  ocean-waters,  are  economically  important, — the  first 
as  -an  article  of  food,  the  second  as  the  source  of  tortoise-shell. 
These  turtles  lay  their  eggs  in  immense  numbers  on  sandy 
beaches  in  holes  dug  for  the  purpose  by  the  female.  As 
many  as  two  hundred  eggs  may  be  laid  by  a  single  female. 
Within  about  six  weeks  they  hatch,  having  been  incubated 
by  the  heat  of  the  sun.  These  turtles  are  captured  by  the 
natives  of  different  parts  of  the  world,  by  diving  or  by  nets  or 
harpoons.  A  peculiar  method  of  capturing  them  is  followed 
by  natives  of  such  widely  separated  regions  as  Torres  Strait, 
Madagascar,  and  Cuba.  This  method  consists  in  utilizing 
the  services  of  the  sucking-fish  (Echene'u),  a  commensal  fish 
provided  with  a  sucker-like  attachment  on  the  top  of  the 
head,  by  means  of  which  it  is  borne  from  place  to  place  by 


358  GENERAL  ZOOLOGY 

larger  fishes,  especially  sharks  and  swordfishes,  leaving  its 
host  occasionally  to  procure  food.  A  string  is  attached  to 
one  of  these  sucking-fishes,  which  is  then  liberated  in  the 
vicinity  of  turtles,  where  it  soon  attaches  itself  to  the  under 


FIG.  183.   Photograph  of  Box-Tortoise 

surface  of  the  shell,  holding  on  so  tenaciously  that  the  turtle 
can  be  drawn  gently  to  the  surface.  The  method  was  noticed 
by  Columbus  or  one  of  his  companions,  and  was  described  in 
1671,  in  Ogilby's  America,  as  follows:  "  Somewhat  further  he 
[Columbus]  saw  very  strange  Fishes,  especially  of  the  G-uaican, 
not  unlike  an  Eel,  but  with  an  extraordinary  great  Head,  over 
which  hangs  a  skin  like  a  bag.  This  Fish  is  the  Natives  Fisher, 
for  having  a  Line  or  handsom  Cord  fastned  about  him,  so 
soon  as  a  Turtel,  or  any  other  of  his  Prey,  comes  above 
Water,  they  give  him  Line  ;  whereupon  the  Gruaican,  like 
an  Arrow  out  of  a  Bowe,  shoots  toward  the  other  Fish,  and 
then  gathering  the  Mouth  of  the  Bag  on  his  Head  like  a 
Purse-net,  holds  them  so  fast  that  he  lets  not  loose  till  hal'd 
up  out  of  the  Water." 

A  common  species  of  tortoise  in  the  eastern  LTnited  States 
is  the  box-tortoise  (Cistu'do,  Fig.  183).    These  tortoises  have 


PINE-LIZARD  AND  ITS  ALLIES:    REPTILIA     359 

a  very  convex  upper  shell  ;  the  lower  portion  is  provided 
with  a  transverse  hinge,  which  makes  it  possible  for  the 
animal  to  bring  the  two  parts  of  the  shell  closely  together, 
thus  forming  a  box,  within  which  are  concealed  head,  neck, 
legs,  and  tail.  A  remarkable  sex-dimorphism  occurs  ;  the 
eyes  of  the  male  are  red,  those  of  the  female,  brown.  More 
flattened  species,  like  the  painted  tortoise  (Chrys'emys)  and 
the  spotted  tortoise  (Nan'emys),  are  better  adapted  to  an 
aquatic  existence. 

Alligators  and  Crocodiles.  The  large  reptiles  known  as  alli- 
gators and  crocodiles  belong  to  the  Crocodil'ia  (Lat.  crocodilus, 
crocodile).  The  heart  in  the  crocodilians  is  highly  specialized, 
having  four  separate  chambers  by  the  complete  separation  of 
the  two  ventricles.  Alligators  (Fig.  184)  differ  from  croco- 
diles in  having  the  canine  teeth  of  the  lower  jaw  fitting  into 
pits  in  the  upper  jaw ;  in  the  crocodiles  they  fit  into  notches 
in  the  side  of  the  jaw.  A  species  of  each  kind  is  found  in 


FIG.  184.  Photograph  of  Alligator 

Florida,  though  both  have  been  sought  so  eagerly  for  the 
teeth  and  skin  that  they  are  now  found  only  in  the  more 
inaccessible  places.  Crocodilians  are  also  found  in  China, 
Africa,  southern  Asia,  and  South  America.  They  frequent 
the  edge  of  rivers,  ponds,  and  lakes,  lying  in  wait  for  their 


360 


GENERAL  ZOOLOGY 


prey  with  only  the  tip  of  the  snout  exposed,  or  concealed  in 
the  vegetation  at  the  edge  of  the  water.  They  feed  at  night, 
and  during  the  day  bask  in  the  sun  on  sand-banks  or  on  logs. 
Geological  Development  of  Reptiles.  We  have  seen  (p.  345) 
that  during  the  Age  of  Amphibians  a  great  part  of  the 
interior  of  North  America  was  one  vast  swamp,  in  which 
stretches  of  black  water  alternated  with  drier  areas  covered 
with  the  characteristic  vegetation  of  the  period,  the  whole 
bathed  in  the  heat  of  a  tropical  climate.  Under  conditions 
similar  to  these  the  reptiles  first  came  into  existence  in  the 
latter  part  of  the  Carboniferous  Age.  They  developed  in  num- 
bers, size,  and  form,  and  became  in  the  succeeding  period  so 
characteristic  a  part  of  the  world's  fauna  that  the  age  is 
named,  from  them,  the  Age  of  Reptiles.  This  forms  the  third 
great  division  of  geological  time,  called  Mesozoic  Time,  or  the 


FIG.  185.  Ceratosaurus 

Era  of  the  Mediceval  Forms  of  Life.  In  North  America  the 
era  began  with  the  upheaval  of  the  Appalachian  system  of 
mountain  ranges,  as  stated  on  page  347.  During  a  part  of 
the  era  great  areas  in  the  south  and  west  were  submerged 
beneath  the  ocean. 


PINE-LIZARD  AND  ITS  ALLIES:    REPTILIA     361 

Fossil  remains  of  the  latter  part  of  the  Carboniferous  Age 
link  the  reptiles  with  the  amphibians,  so  that  it  is  likely  that 
the  former  are  descended  from  a  labyrinthodont  ancestry. 
Some  of  the  reptiles  possessed  certain  skeletal  characteristics 


FIG.  186.  Photograph  of  Model  of  Triceratops 
(American  Museum  of  Natural  History) 

of  the  fur-bearing  animals,  arid  they  are  called  theromorphs 
(beast-formed)  on  that  account. 

On  land  many  species  of  dinosaurs  (terrible  lizard)  were 
found;  some  of  them  were  the  largest  animals  ever  devel- 
oped on  the  earth,  reaching,  in  one  case,  the  possible  length 
of  sixty  or  seventy  feet  and  the  height  of  nearly  twenty 
feet.  This  animal  was  so  great  in  bulk  that  it  is  consid- 
ered hardly  possible  for  it  to  have  supported  such  a  vast 
amount  of  flesh  on  land,  and  it  is  therefore  thought  that  it 
was  aquatic  or  semiaquatic  in  its  habits.  Some  of  the  dino- 
saurs, as  Ceratosau'rus  (Fig.  185),  were  particularly  fitted  to 
walk  on  their  hind  legs,  using  the  tail  as  a  support.  Mem- 
bers of  this  genus  grew  to  be  seventeen  feet  in  height. 
Hundreds  of  the  footprints  of  dinosaurs  have  been  found  in 
the  sandstone  of  the  Connecticut  valley.  Fig.  186  shows  a 
well-known  dinosaur,  Tricer1 'atops,  with  formidable  armature. 


362 


GENERAL  ZOOLOGY 


One  species  reached  a  length  of  more  than  twenty  feet,  and 
stood  eight  feet  high. 

Some  of  the  ancient  reptiles  (the  flying  lizards,  or  ptero- 
saurs, Fig.  187)  were  capable  of  flight  by  means  of  skin 
stretched  between  the  front  and  hind  limbs  and  tail.  Most 
of  the  bones  were  hollow  and  the  skull  was  quite  bird-like. 
Whether  these  characteristics  can  be  taken  to  mean  that 

the  birds  have  de- 
scended from  these 
flying  reptiles  is 
doubtful,  though  it 
has  been  asserted 
by  some  paleontolo- 
gists. It  is  perhaps 
more  likely  that 
these  common 
characteristics  were 
evolved  to  meet 
similar  conditions 
in  two  different 
groups,  and  that  we 
must  look  farther 
back  to  find  the  an- 
cestors of  the  birds. 
Reptiles  which  are 
apparently  related 
to  the  alligators  and  crocodiles,  and  to  the  turtles  and  tor- 
toises, have  also  been  found  in  the  rocks  of  this  period,  so 
that  these  groups  are  very  ancient.  Most  of  the  lizards  and 
snakes  belong  to  a  later  day, 

At  the  close  of  the  Age  of  Reptiles  a  great  upheaval  of 
land  occurred  in  the  west,  forming  the  Rocky  Mountain  sys- 
tem. After  that  disturbance,  which  ranks  in  importance  with 
the  uplift  at  the  close  of  Paleozoic  Time,  practically  the 


FIG.  187.  Restorations  of  Pterosaurs 
(From  Seeley's  Dragons  of  the  Air) 


PINE-LIZARD  AND  ITS  ALLIES:  REPTILIA    363 


whole  of  our  continent,  with  the  exception  of  a  strip  along 
the  South  Atlantic  and  Gulf  coasts,  was  above  the  level  of 
the  sea  (Fig.  188).  During  the  Age  of  Reptiles  a  tropical 
climate  extended  far  toward  the  poles,  but  with  the  upheaval 
of  the  great  land-masses  a  gradual  lowering  of  the  temper- 


FIG.  188.  North  America  after  the  Mesozoic  Upheaval 
(From  Dana's  Manual  of  Geology) 

ature  took  place,  which  affected  the  vegetation.  In  connec- 
tion with  these  changes  occurred  a  wide-spread  destruction 
of  species,  similar  to  that  which  took  place  at  the  close  of 
Paleozoic  Time.  Professor  Dana  says  that  no  American  spe- 
cies of  vertebrate  and  no  marine  invertebrate  is  known  to 
have  lived  both  before  and  after  the  Mesozoic  upheaval. 


CHAPTER   XXVIII 
THE  DOMESTIC  PIGEON 

A  hundred  wings  are  dropt  as  soft  as  one. 
Now  ye  are  lighted  —  lovely  to  my  sight 
The  fearful  circle  of  your  gentle  flight, 
Rapid  and  mute,  and  drawing  homeward  soon  ; 
And  then  the  sober  chiding  of  your  tone 
As  there  ye  sit  from  your  own  roof  arraigning 
My  trespass  on  your  haunts,  so  boldly  done, 
Sounds  like  a  solemn  and  a  just  complaining  ! 

CHARLES  TENNYSON  TURNER,  On  Startling  Some  Pigeons. 

Habitat  and  Distribution.  The  domestic  pigeon  is  known 
under  many  varieties,  all  of  which,  it  is  now  believed,  have 
been  bred  by  artificial  selection  from  the  rock-dove  (Colum'ba 
liv'ia,  Fig.  189),  a  bird  widely  distributed  throughout  the 
European  north-temperate  realm.  In  its  wild  state  the  rock- 
dove  nests  in  the  crevices  of  rocks,  usually  along  seacoasts. 
The  different  domesticated  varieties  have  been  still  more 
widely  scattered  over  the  earth  through  man's  influence. 

External  Structure.  In  the  pigeon  we  can  distinguish  a 
head,  neck,  trunk,  and  tail.  All  over  the  body  the  skin  is 
closely  set  with  feathers.  There  are  two  pairs  of  appendages  : 
the  anterior,  or  wings,  are  used  for  flight,  and  the  posterior, 
the  legs,  for  support.  The  wings  consist  of  an  upper  arm,  fore- 
arm, and  hand,  as  in  the  amphibians  and  reptiles,  though  the 
digits  are  joined  together  and  reduced  in  number  (Fig.  191, 
1,2;  a  third  is  shown,  though  not  numbered).  The  legs  (Fig. 
191,  3)  also  show  divisions  similar  to  the  hind  legs  of  amphib- 
ians and  reptiles,  i.e.  thigh,  lower  leg,  and/t>0£,  the  latter  being 
covered  with  scales  and  ending  in  four  toes,  which  bear  claws 
resembling  those  of  the  lizard. 

364 


THE  DOMESTIC  PIGEON  365 

The  mouth  is  inclosed  by  a  toothless,  horny  beak,  above 
which  are  situated  the  two  nostrils,  set  in  a  mass  of  soft,  fleshy 
skin  called  the  cere  (Fig.  191,  5).  The  eyes  are  large,  and 
have  an  upper  and  a  lower  eyelid  and  a  nictitating  membrane. 
The  external  openings  to  the  ears  are  a  little  behind  and 


FIG.  189.  Photograph  of  Rock-Dove 

below  the  eyes,  and  are  surrounded  with  specially  modified 
feathers.  At  the  base  of  the  tail  on  the  dorsal  surface  is  a 
gland  (Fig.  191,  4)  which  secretes  an  oil  for  keeping  the 
feathers  in  good  condition. 

The  feathers  are  not  scattered  uniformly  over  the  body, 
but  are  arranged  in  definite  tracts  separated  by  areas  in 
which  grow  only  a  few  hair-like  feathers.  As  an  example 


366 


GENERAL  ZOOLOGY 


of  a  fully  developed  feather  we  may  choose  one  of  the  con- 
tour-feathers (Fig.  190,  A)  which  form  the  main  body-covering. 
It  consists  of  a  hollow  base,  the  quill  (Fig.  190,  A,  l),  from 
which  arises  an  expanded  portion  called  the  vane.  Through 
the  center  of  the  vane  runs  the  rachis  (Fig.  190,  A,  2),  which 
gives  off  branches  called  barbs.  From  the  barbs  run  inter- 
locking structures 
(barbules),  bearing 
hooks  which  serve 
to  bind  the  vane 
into  one  continu- 
ous surface.  At 
the  junction  of 
quill  and  rachis  on 
the  under  surface 
of  the  feather  a 
tuft  of  down,  the 
after  shaft  (Fig. 
190,  A,  3),  is  often 
found.  The  wings 
and  tail  bear 
feathers  which  are 
contour-feathers 
of  large  size  and 

with  very  firm 
FIG.  190.  Kinds  of  Feathers  of  Pigeon  0    J  , 

vanes.    Scattered 

A,  contour-feather:  1,  quill  ;  2,  rachis;  3,  aftershaft.      aTnonp,     thp     pfm 
fl.filoplume;   C,  down-feather  *         among 

tour-feathers  are 

down-feathers  (Fig.  190,  Cf),  with  which  the  nestling  pigeon 
was  covered,  and  hair-like  feathers,  orfiloplumes  (Fig.  190,  B). 
Down-feathers  differ  from  contour-feathers  in  having  no 
barbules,  so  that  the  barbs  are  not  held  together,  but 
make  a  fluffy  mass.  Filoplumes  bfrye  only  a  main  axis  with 
few  barbs. 


THE  DOMESTIC   PIGEON  367 

The  Digestive  System.  The  mouth  is  without  teeth.  Sali- 
vary glands  opening  into  the  mouth  furnish  a  fluid  which 
assists  in  swallowing  the  food.  There  is  a  large  tongue 
(Fig.  191,  7),  pointed  at  its  anterior  end.  From  the  pharynx 
there  are  openings  (Fig.  191,  6)  to  the  nostrils  and  to  the 
ears,  as  in  reptiles  and  amphibians.  A  short  oesophagus 
(Fig.  191,  8,  10)  leads  to  a  large  crop  (Fig.  191,  9),  in  which 
the  food,  consisting  largely  of  grain,  is  somewhat  softened 
before  passing  into  the  glandular  stomach  (Fig.  191,  11)  behind 
it.  Glands  in  the  lining  walls  of  the  stomach  pour  out  a 
digestive  fluid  which  serves  to  further  soften  the  food, 
which  then  enters  the  gizzard  (Fig.  191,  12),  an  organ  with 
a  yellow,  horny  lining  surrounded  by  a  thick  mass  of  muscle. 
The  gizzard  contains  small  stones  swallowed  for  the  purpose 
of  assisting  in  grinding  the  food  ;  this  process  is  accomplished 
by  movements  of  the  muscular  walls.  Beyond  the  gizzard 
the  small  intestine  (Fig.  191,  13)  forms  a  loop  inclosing  the 
pancreas  (Fig.  191,  17),  which  discharges  its  secretion  into 
the  intestine  through  three  ducts,  one  of  which  is  shown  in 
Fig.  191,  18.  The  liver  (Fig.  191,  14)  is  large  and  opens  into 
the  intestine  by  two  bile-ducts  (Fig.  191,  15,  16).  At  the  pos- 
terior end  the  intestine  (rectum)  passes  without  change  of 
diameter  into  the  cloaca  (Fig.  191,  20).  The  junction  between 
the  rectum  and  cloaca  is  marked  by  the  presence  of  two  cceca 
(Fig.  191,  19).  The  spleen  (Fig.  191,  21)  is  bright  red,  and  is 
attached  to  the  walls  of  the  glandular  stomach. 

The  Circulatory,  Respiratory,  and  Excretory  Systems.  The 
heart  is  a  large,  four-chambered  organ  inclosed  in  the  peri- 
cardium (Fig.  191,  22).  It  consists  of  two  auricles  and  two 
ventricles,  the  latter  separated  by  a  complete  partition,  as  in 
the  crocodilians.  The  circulation  is  double,  and  the  aerated 
and  non-aerated  blood  come  nowhere  in  contact,  except  in 
the  capillaries.  The  blood  is  sent  to  the  lungs  from  the  right 
ventricle,  through  the  pulmonary  artery  (Fig.  191,  29).  Freed 


THE  DOMESTIC  PIGEON  369 

of  its  carbon  dioxide,  the  blood  returns  through  the  pulmonary 
vein  (Fig.  191,  30)  to  the  left  auricle  (Fig.  191,  23),  whence  it 
passes  to  the  left  ventricle  (Fig.  191,  24)  and  thence  into  the 
aorta  (Fig.  191,  25),  which  distributes  it  to  all  parts  of  the 
body.  The  blood  from  the  body  returns  to  the  right  auricle, 
whence  it  enters  the  right  ventricle,  completing  its  circuit. 
Lymph  circulates  through  the  body  of  the  pigeon  in  vessels 
of  the  lymphatic  system. 

The  organs  of  respiration  are  the  larynx,  which  opens  out 
co  the  pharynx  by  a  slit-like  glottis  (Fig.  191,  31) ;  the  trachea 
•(Fig.  191,  32);  the  bronchial  tubes,  which  ramify  through  the 
tissue  of  the  lungs,  and  the  lungs  themselves  (Fig.  191,  34). 
The  trachea  is  kept  open  by  rings  of  cartilage  in  its  wall. 
At  the  junction  of  the  bronchial  tubes  and  trachea  is  a  slight 
enlargement,  forming  the  syrinx  (Fig.  191,  33),  the  organ  of 
voice.  The  well-known  sounds  are  produced  by  the  vibra- 
tion of  a  fold  of  membrane  at  this  place.  Many  of  the  bones 
are  hollow,  and  there  is  a  system  of  air-sacs  scattered  through 
the  body  and  communicating  with  the  bronchial  tubes.  By 
these  means  the  air  available  for  respiration  is  greatly  increased 
and  the  weight  of  the  body  is  lessened.  Breathing  is  accom- 
plished by  movements  of  the  muscles  of  the  thoracic  region, 
by  which  air  is  driven  almost  completely  out  of  the  lungs  at 
each  expiration.  The  aeration  of  the  blood  is  very  complete, 
and  a  high  temperature,  37°  C.  (100°  F.)  is  maintained. 

The  kidneys  (Fig.  191,  35)  are  dark,  three-lobed  organs 
fitting  closely  into  cavities  beneath  the  back-bone.  The  ureters 
(Fig.  191,  36)  open  into  the  cloaca  (Fig.  191,  37). 

The  Skeletal  System.  The  skull  (Fig.  192,  l)  is  large,  with 
a  comparatively  large,  rounded  cranium  (Fig.  192,  2).  The 
articulation  of  the  cranium  with  the  first  vertebra  is  made 
by  a  single  condyle,  as  in  the  reptiles.  The  vertebrae  of  the 
neck  or  cervical  region  (Fig.  192,  5)  are  free;  those  of  the 
thoracic  region  (Fig.  192,  6),  pelvic  region  (Fig.  192,  7),  and 


370 


GENERAL  ZOOLOGY 


caudal  region  (Fig.  192,  8)  are  more  or  less  united.  There 
are  several  pairs  of  ribs  (Fig.  192,  13).  The  caudal  vertebra 
are  terminated  by  a  peculiar  bone  called,  from  its  shape, 
the  plowshare  bone  (Fig.  192,  9).  The  shoulder-girdle  is 


l — j 


18 


17 


-5 


16 


15  10 


19 


20   21       22 


7 


14---- 


23 


2?       26-— , 


FK 


Skeleton  of  Pigeon.    Reduced 


skull;  2,  cranium;  3,  upper  mandible;  4,  lower  mandible;  5,  cervical  (neck) 
vertebra;;  0,  thoracic  region;  7,  pelvic  region;  8,  caudal  region;  9,  plow- 
share bone  ;  10,  scapula  ;  11,  coracoid  ;  12,  keel  of  sternum  ;  13,  ribs  ;  14,  clav- 
icles (wish-bone);  15,  humerus  ;  10,  radius;  17,  ulna;  18,  thumb;  19,  wrist 
and  hand  bones  (carpometacarpus)  ;  20,  bone  of  third  finger;  21,  bone  of 
second  finger;  22,  end  bone  of  second  finger;  23,  femur;  24,  tibiotarsus; 
25,  fibula  ;  20,  ankle  and  foot  (tarsometatarsus)  ;  27,  bone  of  first  toe  ;  28,  bone 
of  second  toe 


THE  DOMESTIC   PIGEON  371 

composed  of  a  pair  of  narrow  scapulas  (Fig.  192,  10),  to 
which  are  attached  two  coracoids  (Fig.  192,  ll),  connecting 
the  scapulas  and  the  sternum,  and  a  V-shaped  bone,  the  wish- 
bone, formed  from  the  union  of  the  two  clavicles  (Fig.  192,  14). 
A  greatly  enlarged  sternum  with  a  prominent  ridge  or  keel 
(Fig.  192,  12)  serves  as  a  surface  for  attachment  of  the  mus- 
cles of  flight.  The  hip-girdle  is  united  to  the  vertebrae  of 
the  pelvic  region  (Fig.  192,  7).  A  study  of  Fig.  192  and  com- 
parison with  the  skeleton  of  the  frog  (Fig.  165)  will  make 
clear  in  what  respects  the  appendages  are  different. 

The  Nervous  and  Muscular  Systems.  The  brain  is  larger 
in  the  pigeon,  in  proportion  to  the  size  of  the  animal,  than 
in  the  amphibians  and  reptiles.  The  cerebrum  (Fig.  191,  44) 
and  the  cerebellum  (Fig.  191,  46)  are  especially  large.  One 
of  the  principal  functions  of  the  cerebellum  is  to  control  the 
muscles  which  bring  about  the  balancing  of  the  body.  It  is 
apparent  that  this  is  of  greater  importance  in  the  birds  and 
fishes  than  in  the  broader-bodied  amphibians  and  reptiles. 
The  optic  lobes  (Fig.  191,  45),  pressed  to  one  side  by  the  large 
cerebrum,  are  also  well-marked,  in  correlation  with  the 
unusually  large  eyes  and  the  dependence  of  the  pigeon  on 
the  sense  of  sight.  The,  olfactory  lobes  (Fig.  191,  42)  are  rela- 
tively small,  and  the  sense  of  smell  is  not  at  all  keen.  The 
medulla  (Fig.  191,  47)  is  bent  downwards,  as  in  the  reptiles. 

The  muscular  system  shows  many  adaptations  to  the  aerial 
life  of  the  pigeon.  The  great  mass  of  muscle  by  which  the 
downward  stroke  of  the  wings  is  accomplished,  occupies 
almost  all  the  space  on  the  prominent,  keeled  breast-bone. 
Its  position,  low  down  on  the  body,  makes  overturning  in 
the  air  almost  an  impossibility.  The  muscle  which  raises  the 
wing  is  also  situated  beneath  the  breast-bone,  and  is  inserted 
on  the  dorsal  surface  of  the  humerus  by  a  tendon  which 
passes  through  an  opening  at  the  shoulder.  The  tendon  thus 
acts  as  a  pulley  in  raising  the  wing.  The  muscles  which 


372  GENERAL  ZOOLOGY 

bend  the  toes  in  perching  are  so  arranged  that  the  mere 
weight  of  the  bird  keeps  them  contracted,  so  that  even  when 
the  pigeon  is  asleep  the  toes  firmly  grasp  the  perch. 

The  Reproductive  System.  The  spermaries  (Fig.  191,49) 
are  oval  bodies  attached  to  the  kidneys.  The  ovary  of  the 
right  side  is  not  developed,  but  the  left  ovary  is  a  large  organ 
situated  near  the  kidneys. 

Development.  Unlike  most  of  our  domestic  animals,  pigeons 
choose  their  mates  for  life.  After  fertilization  the  ova  or 
"  yolks  "  pass  down  the  oviduct  and  are  covered  with  secre- 
tions from  glands  in  different  regions,  first  with  the  white, 
or  albumen,  then  with  a  thin  membrane,  and  lastly  with  a 
white,  limy  shell.  The  eggs  are  laid  in  a  roughly  made  nest, 
and  are  incubated  by  both  parents  in  turn  for  about  two 
weeks,  when  they  hatch.  The  young  bird  breaks  through 
the  shell  by  means  of  a  hard  structure  on  the  tip  of  its  beak, 
and  makes  its  appearance  covered  with  a  fine  down.  It  is 
interesting  to  note  in  this  connection  that  Darwin  says  that 
some  of  the  short-beaked  tumbler  pigeons,  which  have  been 
developed  by  artificial  selection,  have  beaks  so  short  that  they 
are  unable  to  get  out  of  the  shell  alone,  and  require  therefore 
to  have  the  help  of  the  pigeon-fanciers.  For  a  few  days  after 
hatching  the  young  bird  is  fed  by  both  parents  with  a  milky 
secretion  afforded  by  the  crop,  and  called  "  pigeon's  milk." 

At  first  the  young  are  deaf  and  the  eyes  are  closed,  but 
both  sight  and  hearing  are  acquired  within  a  few  days. 
Professor  T.  Wesley  Mills  of  McGill  University,  Montreal,  has 
found  that  in  newly  hatched  pigeons  the  sensibility  to  touch 
and  pain  is  very  noticeable,  and  that  they  are  extremely  sen- 
sitive to  heat  and  cold.  The  young  birds  rapidly  acquire  the 
power  to  make  coordinated  or  connected  muscular  movements, 
and  in  a  few  days  the  voice  develops.  The  independent  life 
of  the  pigeon,  in  some  cases  Professor  Mills  observed,  began 
about  the  thirty-fourth  day  after  hatching. 


THE  DOMESTIC  PIGEON  373 

Relation  to  Environment.  The  oval  form  of  the  pigeon  is 
well  adapted  to  cleaving  the  air,  and  the  feathers  form  a  light 
waterproof  covering  which  serves  to  retain  the  body-heat  in 
the  rapid  flights  in  the  cold  atmosphere.  A  bird  has  been 
termed  "  an  ocean  greyhound  in  miniature,"  and  the  compar- 
ison is  not  inapt  for  a  creature  which  possesses  such  powers 
of  flight  and  maintains  so  high  a  temperature.  "•  It  is  worthy 
of  notice,"  say  Parker  and  Haswell,  "  that  birds  agree  with 
insects,  the  only  other  typically  aerial  class,  in  having  the 
inspired  air  distributed  all  over  the  body,  so  that  the  aeration 
of  the  blood  is  not  confined  to  the  limited  area  of  an  ordinary 
respiratory  organ."  Other  important  structural  peculiarities 
are  the  light,  toothless  beak,  and  the  small  number  of  digits 
in  the  anterior  extremities.  Still  other  characters  have  been 
referred  to  in  the  discussion  of  the  internal  anatomy. 

The  many  varieties  of  the  domestic  pigeon  afforded  Darwin 
much  material  for  his  book,  The  Variations  of  Animals  and 
Plants  under  Domestication.  From  their  study  he  obtained 
many  of  the  conclusions  which  led  to  the  statement  of  the 
principle  of  natural  selection.  These  domestic  varieties  differ 
among  themselves  in  appearance  far  more  than  many  species 
in  nature.  Some  well-known  varieties  are  the  pouters,  fan- 
tails,  tumblers,  and  carriers.  The  pouters  are  large  birds  with 
elongate  body  and  legs,  and  often  with  inflated  crop  and 
oesophagus.  The  fan  tails  are  known  by  the  extraordinary 
development  of  tail-feathers.  The  tumblers  have  the  remark- 
able habit  of  turning  somersaults  backward  in  the  air  from  a 
considerable  height  nearly  to  the  ground.  The  carriers  have 
the  "  homing  faculty  "  developed  to  such  an  extent  that  they 
are  useful  as  messengers.  Though  shut  within  a  basket  and 
removed  long  distances  from  their  home,  they  have  been  able 
to  find  their  way  back.  Carriers  have  been  used  by  man  for 
many  centuries,  notably  within  recent  times  at  the  siege  of 
Paris  and  in  the  Russo-Japanese  War. 


CHAPTER  XXIX 
THE  ALLIES  OF  THE  PIGEON:    AVES 

Robins  and  mocking-birds  that  all  day  long 

Athwart  straight  sunshine  weave  cross-threads  of  song. 

SYDNEY  LANIER. 

Definition  of  Aves  (Lat.  avis,  a  bird).  The  pigeon  is  a  rep- 
resentative of  the  class  A'ves.  Birds  are  warm-blooded  verte- 
brates adapted  as  a  class  to  an  aerial  existence.  They  are 
covered  with  feathers,  which  are,  in  their  origin,  modified 
scales.  Birds  breathe  by  lungs.  The  young  are  always 
hatched  from  eggs  in  a  form  closely  resembling  the  parent. 
There  is  remarkable  uniformity  of  structure  in  the  class, 
making  classification  extremely  difficult. 

The  following  groups,  which  are  some  of  the  most  impor- 
tant of  the  many  divisions  into  which  birds  have  been  divided, 
are  not  all  entitled  to  rank  as  separate  orders,  though  often 
treated  as  orders. 

The  Ostrich  and  Allies.  The  group  Struthio'nes  (Gr.  struthion, 
ostrich)  contains  the  ostrich  of  Africa,  the  rheas  or  South 
American  ostriches,  and  the  emus  and  cassowaries  of  Aus- 
tralia, New  Guinea,  and  adjacent  islands.  They  are  all  large 
birds  with  rudimentary  wings,  and  with  only  two  or  three 
toes  on  each  foot.  They  have  no  ridge  or  keel  on  the  sternum, 
a  structure  which  in  most  birds  serves  as  an  attachment  for 
the  muscles  of  flight ;  hence  the  struthious  birds  cannot 
fly,  though  there  is  evidence  that  they  have  descended  from 
ancestors  that  had  functional  wings.  The  legs  are  large, 
and  the  birds  run  with  great  speed.  Most  of  them  live  in 
open  desert  places,  though  cassowaries  inhabit  forest  regions. 
The  eggs  are  laid  in  a  deep  depression  in  the  sand,  or  in  a 

374 


THE  ALLIES  OF  THE  PIGEON:  AVES          375 

rough  nest  in  the  case  of  the  cassowary.  The  ostrich  is 
the  best  known  of  the  group,  largely  on  account  of  the 
beautiful  wing  and  tail  plumes,  which  have  been  used  for 
ornaments  from  very  early  times.  Ostriches  are  now  raised 
for  the  sake  of  the  plumes  on  "  farms "  in  California  and 
South  Africa. 

Diving  Birds.    The  group  Pygop'odes  (Gr.  pyge,  the  rump ; 
pous  (pod),  foot)  includes  various  species  of  water-birds  with 


FIG.  193.  Photograph  of  Tern  on  Nest 

webbed  or  lobed  toes.  Their  scientific  name  refers  to  the 
fact  that  the  legs  are  placed  very  far  back,  so  that  when 
standing  an  erect  position  is  assumed.  The  tail  is  very  short. 
The  beak  is  sharp  and  pointed  and  fitted  for  spearing  fishes, 
which  constitute  a  large  part  of  their  food.  They  are  expert 
divers  and  can  swim  under  water  with  only  the  tip  of  the  bill 
exposed.  The  nest  is  generally  nothing  more  than  a  floating 
mass  of  decaying  vegetation,  attached  perhaps  to  some  reeds 
in  shallow  water.  Our  northern  lakes  and  ponds  are  often 
visited  by  the  loon,  a  characteristic  diving  bird. 


376  GENERAL  ZOOLOGY 

Gulls  and  Terns.  The  group  Longipen'nes  (Lat.  longus, 
long ;  penna,  feather)  includes  long-winged  water-birds  with 
sharply  pointed  or  hooked  beaks.  The  colors  are  usually  gray 
above  and  lighter  below.  The  three  front  toes  are  connected 
by  a  web.  These  birds  are  strong  and  graceful  fliers,  and 
spend  much  of  their  time  on  the  wing.  All  the  members  of 
the  group  are  gregarious,  occupying  nesting  sites  on  sandy 
beaches,  in  marshes,  or  on  rocky  shores.  They  obtain  the 
greater  part  of  their  food  from  the  ocean,  and  are  useful  as 
scavengers.  Terns  (Fig.  193)  may  be  distinguished  from 
gulls  by  their  usually  deeply  forked  tail  and  straight  bill. 
Gulls  are  generally  pelagic,  and  they  often  follow  ships  for 
the  sake  of  the  refuse  thrown  overboard ;  terns  frequent 
the  shores  of  both  fresh  and  salt  water.  Owing  to  the 
forked  tail  and  graceful  flight,  the  terns  are  often  called 
sea-swallows. 

Petrels  and  Allies.  The  petrels  and  their  allies  are  strong- 
winged  pelagic  birds,  many  of  which  externally  resemble  the 
gulls  and  terns.  They  may  be  distinguished  from  other  water- 
birds  by  the  nostrils,  which  are  inclosed  in  tubes  lying  on 
the  dorsal  or  lateral  surface  of  the  upper  mandible ;  hence 
their  scientific  name,  Tubina'res  (Lat.  tubus,  tube ;  naris, 
nostril).  The  beak  is  usually  strongly  and  sharply  hooked. 
The  food  consists  of  fishes  and  other  small  animals  which 
live  near  the  surface  of  the  ocean.  The  birds  often  follow 
ships,  like  the  gulls,  to  pick  up  refuse.  They  occupy  various 
nesting  sites  along  shores.  The  wandering  albatross  (Dio- 
mede'a  ex'ulans)  of  southern  oceans  is  the  best-known  species. 
It  is  the  largest  of  sea-birds,  measuring  over  twelve  feet 
between  the  tips  of  the  wings.  One  of  the  traditions  among 
sailors  concerning  the  albatross  is  referred  to  in  Coleridge's 
Ancient  Mariner.  Other  members  of  the  group,  called  stormy 
petrels  and  Mother  Carey's  chickens,  are  also  regarded  by 
many  sailors  with  superstitious  dread. 


THE  ALLIES  OF  THE  PIGEON:  AVES          377 

Pelicans  and  Allies.  The  members  of  the  group  Steganop'- 
odes  (Gr.  steganos,  covered;  pous  (pod),  foot)  differ  from 
all  other  web-footed  birds  in  that  all  four  toes  are  con- 
nected by  a  web  (Fig.  195).  They  are  aquatic,  usually  marine 
birds,  and  feed  mainly  on  fishes.  To  this  group  belong  the 
pelicans  (Fig.  194),  remarkable  for  the  pouch  beneath  the 
bill,  which  is  used  as  a  scoop  to  capture  food  or  as  a  storage 


FIG.  194.  Photograph  of  White  Pelican 

reservoir.  There  are  about  a  dozen  species  of  pelicans  distrib- 
uted over  the  world,  of  which  two  species,  the  brown  and  the 
white  pelican,  occur  within  the  limits  of  the  United  States. 
White  pelicans  (Fig.  194)  have  the  habit  of  surrounding 
schools  of  small  fishes  and  driving  them  with  loud  beatings 
of  wings  into  shallower  water,  where  they  can  be  scooped  up 
in  the  great  pouch  and  devoured  at  leisure.  The  figure  shows 
the  peculiar  horny  outgrowth  which  appears  on  the  bill  of 
the  male  at  the  breeding-season. 

Ducks,  Geese,  and  Swans.  The  group  An' seres  (Lat.  anser, 
goose)  is  made  up  of  water-birds  which  have  the  three  front 
toes  webbed  and  the  tail  comparatively  well-developed.  The 


378 


GENERAL  ZOOLOGY 


FIG.  195.  Foot  of  Pelican 


ducks,  geese,  and  swans  are  included  here.  The  bill  is  usually 
flattened  and  is  furnished  with  transverse  tooth-like  ridges 

on  both  upper  and  lower  mandibles. 
In  the  species  which  frequent  rivers 
and  ponds,  feeding  largely  on  vege- 
table food  or  on  small  mollusks, 
crustaceans,  and  larvse  of  insects, 
these  ridges  act  as  a  strainer 
through  which  the  water  runs  off 
when  the  bill  is  closed,  leaving  the 

rL  Vm  ^00(*  Behind;    in   the   harbor  and 

1 i     TO  sea-haunting,  fish-eating  species  the 

ridges  are  useful  in  holding  the 
slippery  food.  The  nest  is  usually 
placed  on  the  ground  near  the  water. 
Several  of  the  swans  have  the 
trachea  greatly  lengthened  and 
looped  through  the  hollow  sternum  (Fig.  196).  By  this  means 
they  produce  their  loud  whistling  or  trumpeting  note.  Wild 
geese  have  long  excited  interest  on  account  of  their  peculiar 
manner  of  migrat- 
ing in  a  flock  ar- 
ranged in  a  long, 
V-shaped  group, 
keeping  up  the 
continual,  sono- 
rous "honk,  honk." 
Among  the  geese 

and   swans    the 

FIG.  196.  Trachea  of  Trumpeter  Swan 
sexes  are  usually 

alike,  but  in  many  of  the  ducks  the  male  is  specially  orna- 
mented with  brilliantly  colored  plumage.  Well-known  species 
of  ducks  are  the  canvasback  duck,  dear  to  the  epicure ;  and 
the  mallard,  the  ancestor  of  the  common  domesticated  duck. 


THE  ALLIES  OF  THE  PIGEON:  AVES 


379 


Herons,  Storks,  and  Allies.  The  birds  of  the  group  Hero- 
dio'nes  (Or.  erodios,  heron),  often  spoken  of  as  wading  birds, 
are  long-legged  species,  with  four  toes  placed  on  about  the 
same  level,  and  slightly  or  not  at  all  webbed.  The  bill  and 
neck  are  long  and  slender.  Crests  and  decorative  plumes 
often  ornament  the  head  and  neck.  Herons  haunt  the  edge 


FIG.  197.  Photograph  of  Egrets 

of  ponds,  lakes,  and  rivers,  where  they  feed  on  fishes  and 
frogs,  which  they  capture  with  their  long,  sharp  beaks. 
They  nest  in  great  colonies,  usually  in  trees.  The  nests 
are  clumsy  affairs  made  of  sticks  in  an  untidy  mass.  One 
of  our  largest  species  is  the  great  blue  heron  which  stands 
nearly  five  feet  high.  Several  herons,  called  egrets  (Fig.  197), 
which  have  the  misfortune  to  grow  beautiful  dorsal  plumes, 
or  "  aigrettes,"  at  the  breeding-season,  have  been  practically 
exterminated  by  man  for  the  sake  of  their  plumes  for  women's 
hats.  These  birds  were  formerly  common  in  Florida  and  along 


380  GENERAL  ZOOLOGY 

the  Gulf  coast.  Storks  are  natives  of  the  Old  World,  fre- 
quenting wooded  regions  or  open  country.  The  white  stork 
has  been  tamed  in  some  countries,  where  it  frequently  occu- 
pies nesting  sites  on  houses. 

Cranes  and  Allies.  Though  superficially  like  the  herons,  in 
that  they  have  a  long  bill,  neck,  and  legs,  the  cranes  and 
their  allies  may  nevertheless  be  distinguished  from  the  herons 
by  the  elevation  of  the  hind  toe  above  the  level  of  the  others. 
The  cranes  are  scattered  widely  over  the  globe,  though  we 
have  but  three  species  in  North  America.  They  frequent 
marshes  and  open  plains  (their  scientific  name,  Paludic'olce, 
means  marsh-inhabitant),  and  feed  on  both  vegetable  and  ani- 
mal food,  the  latter  consisting  largely  of  small  reptiles  and 
amphibians.  "  Erect  and  tall,  they  may  be  seen  striding 
swiftly  along  with  head  thrown  back,  or  strutting  around 
their  mates;  while  in  spring  they  often  stand  in  rows  and 
proceed. to  stalk  about  in  single  file,  or  dance  to  meet  one 
another  with  nodding  heads,  necks  advanced,  and  wings 
widely  outspread.  Thereafter  they  bow  toward  the  ground, 
jump  in  the  air,  and  perform  graceful  antics  of  all  descrip- 
tions. The  chosen  spot  for  these  dances  is  commonly  near 
water.  The  male  courts  his  spouse  in  somewhat  similar 
fashion,  and  twigs  or  feathers  are  often  tossed  in  the  air  in 
sport,  to  be  caught  again  ere  they  touch  the  ground"  (Cam- 
bridge Natural  History,  Vol.  IX). 

Snipes,  Sandpipers,  Plovers,  and  Allies.  The  well-known 
shore-birds,  included  in  the  group  Limic'olce,  usually  have 
long,  slender  legs,  with  the  hind  toe,  when  present,  elevated 
above  the  others.  The  scientific  name  refers  to  their  habitat, 
(Lat.  limus,  mud  ;  colere,  to  dwell).  The  bill  is  usually  long 
and  slender  and  more  or  less  soft,  especially  at  the  tip.  With 
their  bills  these  birds  probe  the  mud  and  sand  of  pond  and 
river  margins  and  the  seacoast  for  their  food,  which  consists 
of  small  crustaceans,  worms,  and  mollusks.  The  plumage  is 


THE  ALLIES  OF  THE  PIGEON  :  AVES 


381 


usually  brown  or  gray,  with  some  white  intermixed.  During 
the  breeding-season  many  species  give  utterance  to  more  or 
less  musical  cries.  At  other  seasons  a  number  of  species 
have  shrill  call-notes  or  whistles.  The  eggs  are  usually  laid 
on  the  sand  in  a  hollow  scraped  for  the  purpose.  They  are 
very  often  protectively  colored.  Like  the  domestic  fowl,  the 
young  are  able  to  take  care  of  themselves  from  the  very  first. 
Their  nestling  plumage  is  also  protectively  colored. 

One  of  the  best  known  is  the  woodcock,  which  frequents 
low,  moist,  wooded  regions.  The  tip  of  the  upper  mandible 
can  be  moved  upward,  so  that  it  is  of  use  in  feeling  for  and 
seizing  worms  in  the  ground.  The  Wilson's  snipe  of  fresh- 
water meadows  and  swamps,  and  the  upland  plover  of  higher 
and  drier  pastures,  are  other  familiar  species. 

Grouse,  Quail,  Turkeys,  Pheasants,  and  Allies.  The  galli- 
naceous birds,  G-alli'nce  (Lat.  gallina,  hen),  commonly  known 
as  scratching  birds, 
have  a  stout,  convex 
beak  fitted  for  seizing 
and  crushing  seeds, 
which  form  a  large 
part  of  their  food ;  the 
wings  are  short  and 
rounded,  and  the  short, 
stout  legs  have  strong 
toes  adapted  to  scratch- 
ing. Nearly  all  species 
are  terrestrial  in  habit. 
Here  are  included  the 
larger  part  of  the  game- 
birds  of  the  world.  By  far  the  best  known  of  the  group  is 
our  domestic  fowl,  of  many  races,  all  of  which  are  descended 
from  the  red  jungle-fowl  (Gal'lus  banki'vus,  Figs.  198,  199) 
of  India,  Sumatra,  Celebes,  and  the  Philippines. 


FIG.  198.  Photograph  of  Jungle-Fowl 


382 


GENERAL  ZOOLOGY 


FIG.  199.  Young  of  Jungle-Fowl 


The  best  known  of  the  grouse  in  the  eastern  United  States 
is  the  ruffed  grouse  (Bona'sa  umbel' lus),  usually,  but  wrongly, 
called  "  partridge  "  in  New  England.  It  is  about  the  size  of 

the  domestic  fowl,  and  has  pro- 
nounced black  ruffs  on  the  sides 
of  the  neck.  The  male  produces 
a  loud  drumming  sound  by  beat- 
ing the  air  rapidly  with  the  wings. 
The  sound  is  a  call  to  the  female, 
though  it  is  indulged  in  occa- 
sionally at  other  seasons  than  in 
the  spring.  The  quail-like  bob- 
white  (Coli'nus  Virginia' nus)  is 
also,  but  erroneously,  called  "par- 
tridge "  in  the  southern  states.  It  is  a  smaller  bird  than  the 
ruffed  grouse,  reddish  brown  in  color,  and  without  the  ruff 
about  the  neck.  Neither  of  these  birds  should  be  called 
"partridge,"  since  that  name  is  already  in  use  for  Eurasian 
species  of  gallinaceous  birds.  The  same  statement  is  true  of 
the  term  "  quail,"  which  is  often  applied  to  our  bob- white. 
The  pheasants  are  magnificently  colored  birds,  native  to 
southeastern  Asia  and  adjacent  islands. 

Pigeons  and  Doves.  The  Colum'bce  (Lat.  columba,  a  dove) 
are  closely  related  to  the  gallinaceous  birds,  but  the  nostrils 
open  into  a  fleshy  cere.  We  have  in  the  eastern  United 
States  several  species  of  wild  doves,  and  the  passenger-pigeon 
(Ectopis'tes  migrato'rius}.  The  latter  were  formerly  present  in 
immense  numbers  in  the  wooded  regions  of  the  eastern  United 
States.  In  the  early  years  of  the  eighteenth  century  flocks 
were  seen  that  stretched  far  across  the  sky,  and  which 
required  hours  to  pass  a  given  point.  Farmers  were  in  some 
places  obliged  to  watch  their  fields  constantly  to  prevent  the 
birds  from  picking  up  the  sowed  grain.  The  birds  nested  in 
great  colonies  of  thousands,  sometimes  as  many  as  forty  nests 


THE  ALLIES  OF  THE  PIGEON:  AVES 


383 


FIG.  200.  Head  of  Golden  Eagle 


in  a  single  tree.  Owing  to  the  increased  demand  for  both 
young  and  adults  as  food  they  were  slaughtered  indiscrimi- 
nately and  have  since 
been  nearly  extermi- 
nated. 

Hawks,  Eagles, 
Owls,  and  Vultures. 
The  Rapto'res  (Lat. 
raptor,  robber)  are 
generally  spoken  of 
as  birds  of  prey, 
though  the  term  is 
equally  applicable  to 
some  members  of 
other  groups,  the 
gulls  among  the  long-winged  swimmers,  for  example.  The 
beak  is  stout,  strong,  and  sharply  hooked  (Fig.  200);  the  toes, 

arranged  three  in  front  and  one 
behind,  are  provided  with  strong, 
sharp,  curved  claws  (Fig.  201) 
with  which  to  seize  their  living 
prey,  except  in  the  vultures, 
which  feed  on  carrion.  The 
Raptores  possess  great  powers 
of  flight.  The  female  is  larger 
than  the  male.  The  nests  are 
generally  bulky  structures,  com- 
posed of  sticks  and  placed  in 
tall  trees  or  on  rocky  cliffs. 

The  red-tailed  and  the 
red-shouldered  hawks  are  gener- 
ally termed  "  hen-hawks  "  or  "  chicken-hawks  "  by  farmers. 
Though  they  occasionally  levy  tribute  on  the  chicken-yard, 
their  propensities  in  this  direction  are  not  so  marked  as  is  the 


FIG.  201.  Claw  of  Golden  Eagle 


384 


GENERAL  ZOOLOGY 


case  with  some  of  the  other  hawks  which  do  not  sail  so  con- 
spicuously in  the  air.  Hen-hawks  undoubtedly  do  more  good 
than  harm  by  destroying  large  numbers  of  mice  and  other 
small  mammals.  The  vultures  are,  generally  speaking,  scav- 
engers, or  they  may  attack  weak  and  disabled  animals.  The 
black  vulture  and  the  turkey-buzzard  are  invaluable  as  scav- 
engers in  the  southern  states.  They  have  been  protected  for 

this  reason,  and  have 
become  very  tame  in 
many  places.  The 
owls  (Fig.  202)  are 
adapted  to  nocturnal 
life.  The  plumage  is 
soft,  making  possible 
a  noiseless  flight  ;  the 
eyes  are  large,  and 
placed  so  that  they 
look  forward. 

Parrots  and  Cock- 
atoos. The  Pait'taci 
(Gr.  psittakos,  parrot) 
are  generally  birds  of 

Colors'   with  a 


u.  202.  Photograph  of  Barred  Owl 

very   stout,    strongly 

hooked  beak,  which  is  used  for  climbing,  as  well  as  for 
crushing  seeds.  They  have  four  toes,  arranged  two  in  front 
and  two  behind,  with  strong,  curved  claws.  Most  species 
inhabit  forests  ;  they  are  all  good  climbers.  A  great  many 
species  can  learn  to  talk,  but  the  red-tailed  gray  parrot  of 
Africa  is  considered  the  best  talker.  The  cockatoos  (Fig. 
203)  are  often  ornamented  with  crest-feathers  of  various 
colors.  They  are  restricted  to  Australia,  Tasmania,  and 
the  Philippines.  A  New  Zealand  parrot,  the  kea  (Nes'tor 
notab'ilis),  has  of  late  years  become  carnivorous  in  its  habits, 


THE  ALLIES  OF  THE  PIGEON  :  AVES 


385 


alighting  on  the  backs  of  live  sheep  and  digging  deep  into 
the  flesh  for  the  fat  surrounding  the  kidneys.  "  The  pro- 
pensity is  said  to  have  originated  from  the  bird  pecking 
at  sheepskins  hanging  outside  country  stations."  We  have 
only  one  member  of  the  group  in  the  United  States,  the 
Carolina  paroquet,  and  that  has  been  almost  exterminated. 

Woodpeckers.  The  group  Pi'ci  (Lat.  picus,  a  woodpecker) 
forms  a  well-marked 
assemblage  of  climb- 
ing birds,  with  two 
toes  in  front  and 
two  behind  (except 
in  the  three.-toed 
woodpeckers). 

Woodpeckers  have 
a  strong,  straight  bill, 
with  which  they  dig 
into  wood  for  insects, 
and  a  long,  barbed 
tongue,  spear-pointed 
at  the  end,  which 
enables  them  to 
draw  their  food  from 
beneath  the  bark  of 
trees.  The  tail-feathers  are  usually  stiff  and  pointed,  and 
form  a  support  to  rest  on  while  the  bird  is  engaged  in 
feeding.  The  usual  coloration  in  the  group  is  black  and 
white,  but  red  often  appears  on  the  head.  The  nests  are 
made  in  holes  in  trees,  and  the  eggs  are  white  in  color. 
By  far  the  greater  number  of  the  woodpeckers  are  beneficial 
to  the  farmer,  but  the  yellow-bellied  woodpecker,  or  sap- 
sucker  (Spliyrapi' cus  va'rius,  Fig.  204),  girdles  trees  with 
numerous  small  holes  to  get  at  the  sap  beneath  the  bark. 
The  golden- winged  woodpeckers  (Colap'tes)  have  lost  some 


FIG.  203.  Photograph  of  Cockatoo 


386 


GENERAL  ZOOLOGY 


of  the  habits  of  the  family,  and  have  descended  to  picking 

up  part  of  their  food  on  the  ground  of  fields  and  pastures. 

Perching  or  Singing  Birds.    The  passerine  type  (Lat.  passer, 

sparrow)  is  exemplified  in  more  than  half  the  birds  of  the 


FIG.  204.   Photograph  of  Yellow-Bellied  Woodpeckers 
(American  Museum  of  Natural  History) 

world.  The  characteristics  which  serve  to  distinguish  the 
Pas' seres,  or  perching  birds,  from  other  groups  are  the  pres- 
ence of  four  toes  without  webs,  placed  at  the  same  level, 
three  in  front  and  one  behind.  The  perchers  are  birds  of 


THE  ALLIES  OF  THE  PIGEON  :  AVES 


387 


small  or  medium  size.    Among  them  are  included  all  our 
well-known  songsters.    The  nesting-habits  are  various,  but  a 


FIG.  205.  Nest  of  Catbird 

great  number  build  complicated  and  often  beautiful  nests 
(Fig.  205)  in  which  to  rear  their  young.  The  young  when 
hatched  are 
always  in  a 
helpless  condi- 
tion, requiring 
the  care  of  the 
parent  for  a 
time  (compare 
Figs.  206  and 
199).  The  sexes 
may  be  alike,  or 
the  male  may 


FIG.  206.  Youns;  of  Catbird 


be    specially 

ornamented. 

The  bright  colors  of  the  male  are  generally  believed  to  be 

due  to  sexual  selection,  and  his  ability  to  sing  is  accounted 


388 


GENERAL  ZOOLOGY 


for  in  a  similar  manner.  It  is  worthy  of  notice  that  in  those 
cases  where  song  has  been  developed,  bright  colors  are  usu- 
ally absent.  The  perching  birds  are  the  familiar  birds  of 
forest,  field,  and  garden,  and  are  those  with  which  the  young 
student  will  naturally  begin  his  study  in  the  field.  They  are 
so  numerous  that  very  few  can  be  referred  to  here. 

The  flycatchers  (Tymn'nidm,  Fig.  207)  are  pert  little  birds 
with  a  slightly  hooked  bill,  provided  with  bristles  at  its  base. 
From  some  convenient  perch  they  watch  for  insects,  which 


FIG.  207.  Photograph  of  Mounted  Group  of  Flycatchers 
(American  Museum  of  Natural  History) 

they  snap  at  on  the  wing,  returning  to  the  perch  after  each 
flight.  The  bristles  at  the  base  of  the  bill  serve  to  entangle 
insects  and  make  their  capture  more  certain.  The  brightly 
colored  wood- warblers  (Mniotil'tidce),  as  Mr.  Chapman  says, 
"  at  once  the  delight  and  the  despair  of  field  students,"  are 
also  insect-eaters,  getting  their  food  almost  exclusively  from 
the  leaves  or  bark  of  trees,  though  some  capture  it  on  the 
wing,  after  the  manner  of  the  flycatchers. 

The  vireos  (Vir eon' idee)  are  to  be  found  in  much  the  same 
places  as  many  of  the  wood-warblers,  industriously  picking 
insects  from  the  leaves  of  trees,  or  from  crevices  in  the  bark. 


THE  ALLIES  OF  THE   PIGEON:   AVES          389 

Vireos  are  small,  greenish-colored  birds,  which  build  cup- 
shaped,  hanging  nests  of  plant-fibers,  lined  with  pine-needles 
and  similar  material.  The  white-eyed  vireo  has  the  habit  of 
often  weaving  a  piece  of  newspaper  into  the  structure  of  its 
nest ;  hence  it  is  called  "  the  politician  "  in  some  parts  of  the 
country.  A  cast  snake's  skin  is  also  a  favorite  object  for  this 
purpose. 

Our  familiar  crow  and  our  almost  equally  familiar  blue  jay 
are  members  of  the  family  Cor'vidce.  The  family  is  considered 
by  ornithologists  to  be  unusually  intelligent,  and  by  some  is 
even  considered  the  highest  bird-group.  Closely  allied  to  the 
crows  and  jays  are  the  blackbirds  and  orioles  (Icter'idce).  In 
this  family  is  the  cowbird,  which  has  the  habit  of  laying  its 
eggs  in  the  nests  of  other  birds,  which  are  usually  smaller 
than  itself,  and  of  leaving  the  egg  to  be  hatched  by  its  foster- 
parent.  A  South  American  cowbird  lays  its  eggs  in  the  nest 
of  another  species  of  cowbird,  which  does  not  possess  this 
parasitic  habit  fully  developed,  since  it  sometimes  builds  its 
own  nest  and  sometimes  lays  its  eggs  in  the  nests  of  other 
birds.  The  orioles  are  remarkable  for  their  elaborately  inter- 
woven hanging  nests,  much  deeper  than  the  somewhat  similar 
hanging  nests  of  the  vireos. 

The  finches  and  sparrows  (Fringil'lidoe)  are  the  largest 
family  of  birds.  However  varied  the  members  of  this  group 
are  in  form  and  color,  they  agree,  usually,  in  the  possession 
of  a  stout,  conical  bill,  adapted  to  crushing  seeds.  The 
European  house-sparrow,  often  called  the  English  sparrow 
(Pas'ser  domes'ticus),  is  probably  well  known  to  dwellers  in 
nearly  every  town  and  city  in  the  United  States.  Intro- 
duced from  Europe  into  this  country  in  the  neighborhood  of 
Brooklyn,  in  1851  and  1852,  the  house-sparrow  has  since 
spread  so  widely  that  it  may  now  be  said  that  its  conquest 
of  the  centers  of  population  in  our  country  is  almost  com- 
plete. It  has  made  itself  at  home  in  our  city  streets,  and 


390  GENERAL  ZOOLOGY 

has  managed  to  pick  up  a  living  where  another  bird  would 
starve  to  death.  Most  of  the  sparrows  belong  to  the  fields 
and  hedges,  where  their  brownish  coloration  serves  to  make 
them  inconspicuous. 

Our  American  robin  belongs  to  the  family  of  thrashes 
(Tur'didcu).  Though  not  a  gifted  songster,  like  some  of  its 
near  relatives,  the  robin  is  dear  to  all  dwellers  in  the  country. 
With  the  bluebird  and  the  song-sparrow  it  shares  the  honor 
of  being  spring's  harbinger  among  the  birds  in  eastern  North 
America.  Its  habits,  song,  and  call-notes  offer  an  interesting 
subject  for  study. 

Migration  of  Birds.  The  phenomena  of  migration  are  espe- 
cially noteworthy  among  birds,  and  the  birds  of  a  region  may 
be  roughly  classified  in  connection  with  this  habit.  Those 
species  which  remain  in  a  region  all  the  year  are  spoken  of 
as  permanent  residents  of  that  region.  They  may  be  more 
or  less  migratory  as  individuals ;  that  is,  the  birds  seen  in 
the  summer  may  not  be  the  same  individuals  that  appear 
in  the  autumn  or  winter.  The  great  majority  of  the  birds 
of  the  northern  hemisphere  leave  in  the  autumn  to  pass  the 
winter  in  the  south,  returning  in  great  bird  waves  in  the 
spring.  These  birds  are  the  summer  residents  of  the  region. 
The  summer  residents  of  the  eastern  United  States  may 
pass  the  winter  in  the  southern  states,  or  they  may  (like  the 
bobolink)  go  as  far  as  Brazil.  When  the  great  hordes  of  the 
summer  residents  have  passed  to  the  south,  other  birds  come 
down  from  the  north;  these  are  ivinter  visitants.  Often  a 
bird  loses  its  way,  or  is  blown  out  of  its  regular  line  of  travel 
to  other  regions ;  such  birds  are  accidental  visitants  to  those 
regions. 

The  great  migratory  movements  of  birds  are  fairly  regular 
year  after  year,  and  they  are  participated  in  by  thousands 
upon  thousands  of  individuals.  When  the  appropriate  time 
comes  each  species  gathers  in  large  flocks,  or  the  individuals 


THE  ALLIES  OF  THE  PIGEON  :  AVES          391 

separately  move  off  on  their  long  trip.  The  larger  birds,  with 
special  means  of  defense,  as  the  large  hawks  and  cranes  or 
those  species  with  untiring  flight,  as  the  ducks,  choose  day- 
light in  which  to  travel.  Some  of  the  smaller  birds  which 
are  also  rapid  and  untiring  fliers,  like  the  swallows,  also 
carry  on  their  migrations  during  the  day,  but  most  of  the 
smaller  birds  migrate  at  night.  A  foggy  night  causes  the 
death  of  large  numbers  of  birds ;  over  fifteen  hundred  indi- 
viduals have  been  picked  up  at  the  foot  of  Bartholdi  Statue 
in  New  York  Harbor  after  a  dark  night  in  the  migration 
period.  Attracted  by  the  bright  light  the  birds  had  dashed 
against  the  glass  in  their  swift  flight.  Birds  are  exposed  to 
other  dangers  on  their  migration-flight.  They  are  fed  upon 
by  other  animals,  and  many  perish  from  fatigue,  or  are  blown 
out  to  sea,  where  they  fall  exhausted  into  the  water. 

It  is  not  thoroughly  understood  how  birds  find  their  way 
over  such  great  stretches  of  territory.  The  "  fly-lines "  of 
some  swallows  are  ten  thousand  miles  long.  The  golden 
plover  breeds  in  arctic  America  and  winters  in  Patagonia. 
By  some  ornithologists  (students  of  birds)  the  ability  to 
travel  these  great  distances  is  ascribed  to  the  possession  of 
a  sixth  sense,  —  that  of  direction,  which  seems  to  be  pos- 
sessed by  some  other  animals  and  by  savage  man.  It  is 
supposed  that  somehow  the  nervous  system  registers  the 
ground  passed  over.  Observations  by  American  ornitholo- 
gists seem  to  show  that  the  old  birds  lead  the  way.  Some 
birds  keep  up  a  continual  calling  to  each  other,  which  may 
help  to  keep  the  members  of  the  flock  together.  In  following 
their  migration-routes  birds  have  undoubtedly  been  helped  in 
some  cases  by  the  rivers  and  coast-lines,  and  in  Europe  there 
are  cases  where  the  fly-lines  mark  submerged  coast-lines  which 
the  birds  followed  when  the  land  was  above  the  water.  There 
is  such  a  line  between  England  and  the  continent,  and  another 
across  the  Mediterranean  Sea. 


392  GENERAL  ZOOLOGY 

The  causes  which  underlie  these  great  movements  cannot 
yet  be  stated  with  absolute  certainty.  The  southerly  migra- 
tion is  probably  to  be  associated  in  general  with  the  failure 
of  the  food-supply  and  the  decrease  in  temperature.  It  has 
been  stated  that  the  return  to  the  north  is  due  to  the  desire 
of  the  birds  to  regain  their  old  home,  or  to  their  desire  for 
seclusion  during  the  breeding-season.  The  origin  of  the 
habit  has  undoubtedly  to  be  looked  for  in  the  geological 
history  of  the  world.  During  the  Glacial  Epoch  (see  p.  431) 
a  great  part  of  the  northern  hemisphere  was  shrouded  in  a 
mass  of  ice,  which  came  down  from  the  north  upon  a  region 
which  was  then  almost  tropical  *ink  its  climate.  With  the 
onward  advance  of  the  ice,  the  birds,  like  all  other  forms  of 
life,  were  driven  south,  returning  whenever  the  melting  of 
the  ice  permitted.  Geology  tells  of  many  periods  of  alter- 
nate progression  and  regression  of  the  ice-sheet,  with  accom- 
panying changes  of  climate.  We  have  already  spoken  of  the 
discontinuous  distribution  of  the  White  Mountain  butterfly 
(see  p.  48)  as  dating  from  this  period.  It  may  well  be  that 
the  northerly  and  southerly  movements  then  begun  among 
the  birds  have  been  continued  till  to-day. 

Economic  Importance  of  Birds.  Leaving  out  of  considera- 
tion their  value  to  man  as  a  source  of  food,  birds  are  chiefly 
important  economically  in  connection  with  their  destruction 
of  insects  injurious  to  vegetation.  Of  course  not  all  birds 
are  beneficial  in  this  respect ;  whether  they  are  beneficial  or 
injurious  depends  largely  on  the  character  of  their  food. 
What  we  know  of  the  food  of  birds  has  come  not  only  from 
the  observation  of  the  birds  in  the  field  but  also  from  the 
examination  of  the  contents  of  their  stomachs.  The  Division 
of  Biological  Survey  of  the  Department  of  Agriculture  has 
performed  a  most  useful  task  in  collecting,  tabulating,  and 
publishing  observations  from  all  parts  of  the  country,  and 
has  recently  supplemented  this  general  work  by  a  study  of 


THE  ALLIES  OF  THE  PIGEON:  AVES          393 

the  economic  conditions  of  a  single  area.  The  tract  chosen 
was  a  farm  of  about  two  hundred  and  thirty  acres  on  the 
Potomac  River  in  Maryland,  just  opposite  Mount  Vernon. 
Here  observations  were  made  on  the  bird  and  insect  life  of  the 
farm,  with  the  view  of  determining  not  only  what  the  birds 
really  did  eat  but  also  what  food  was  available  for  them  at 
different  seasons.  So,  too,  the  vertebrate  life  of  the  farm,  — 
the  mice,  poultry,  and  game,  which  form  a  part  of  the  food 
of  some  birds;  the  fruit,  both  wild  and  cultivated;  the  grain 
and  the  weeds  of  the  region,  and  the  crops  that  were  planted ; 
all  these  were  considered  in  the  investigation.  Besides  obser- 
vations on  the  living  birdsJflhe  stomachs  of  six  hundred  and 
forty-five  specimens  were  examined.  As  in  other  investiga- 
tions along  the  same  line,  it  was  found  that  the  largest  con- 
sumption of  insects  is  to  be  credited  not  to  the  adult  but  to 
the  nestling.  As  several  broods  are  raised  by  many  birds 
each  year,  and  each  young  bird  requires  at  first  considerably 
more  than  its  own  weight  of  food  in  a  day,  the  number  of 
insects  destroyed  in  this  way  is  almost  incalculable.  Of  course 
some  beneficial  insects  are  included  in  this  list,  but  it  has 
been  found  that  those  insects  which  are  to  be  classed  as  cer- 
tainly useful,  as  some  of  the  bees,  wasps,  and  beetles,  which 
prey  on  pests,  make  up  a  very  small  proportion  of  the  food. 
The  diagram  (Fig.  208)  shows  the  proportion  of  different  sorts 
of  food  in  the  young  and  the  adult  of  the  common  crow. 

Some  of  the  conclusions  of  Dr.  Judd,  who  studied  this  region 
for  the  Biological  Survey,  are  that  "  the  English  sparrow,  the 
sharp-shinned  and  Cooper  hawks,  and  the  great  horned  owl 
are,  as  everywhere,  inimical  to  the  farmers'  interests  and 
should  be  killed  at  every  opportunity.  The  sapsucker  punc- 
tures orchard  trees  extensively  and  should  be  shot.  The 
study  of  the  crow  is  unfavorable  in  results  so  far  as  these 
particular  farms  are  concerned,  partly  because  of  special  con- 
ditions. Its  work  in  removing  carrion  and  destroying  insects 


GENERAL  ZOOLOGY 

is  serviceable,  but  it  does  so  much  damage  to  game,  poultry, 
fruit,  and  grain  that  it  more  than  counterbalances  the  good, 
and  'should  be  reduced  in  numbers.  The  crow-blackbird 
appears  to  be  purely  beneficial  to  these  farms  during  the 


7  days  or  less 


1  to  2  weeks  old 


BEETLES     ^VERTEBRATES 


3  weeks  and  older  adult 

FIG.  208.  Diagram  of  Crow-Food 
(From  Judd's  Birds  of  a  Maryland  Farm) 

breeding-season,  and  feeds  extensively  on  weed-seed  during 
migration,  but  at  the  latter  time  it  is  very  injurious  to  grain. 
The  remaining  species  probably  do  more  good  than  harm  and, 
except  under  unusual  conditions,  should  receive  encourage- 
ment by  the  owners  of  the  farms.  Certain  species,  such  as 


THE  ALLIES  OF  THE  PIGEON:   AVES          395 

flycatchers,  swallows,  and  warblers,  prey  to  some  extent  upon 
useful  parasitic  insects ;  but  on  the  whole  the  habits  of  these 
insectivorous  birds  are  productive  of  considerable  good  to 
man.  Together  with  the  vireos,  cuckoos,  and  woodpeckers 
(exclusive  of  the  sapsuckers),  they  are  the  most  valuable  con- 
servators of  foliage  on  the  farms.  The  quail,  meadow-lark, 
orchard-oriole,  mocking-bird,  house-wren,  grasshopper-sparrow, 
and  chipping  sparrow  feed  on  insects  of  the  cultivated  fields, 
particularly  during  the  breeding-season,  when  the  nestlings 
of  practically  all  species  eat  enormous  numbers  of  caterpillars 
and  grasshoppers." 

Bird-Protection.  The  first  steps  toward  bird-protection 
were  taken  at  the  instance  of  the  sportsmen,  in  whose  inter- 
est laws  were  passed  prohibiting  the  destruction  of  game- 
birds  except  at  stated  seasons  of  the  year.  These  laws  were 
in  the  interest,  too,  of  the  hunter  who  shot  for  the  market, 
since  they  secured  for  the  birds  freedom  from  the  molesta- 
tion of  man  during  the  period  of  bringing  up  their  young, 
without  which  protection  their  extinction  would,  in  many 
cases,  have  been  only  a  matter  of  time.  Of  late  years  great 
interest  has  been  aroused  in  ornithology,  and  the  value  of 
birds  to  agriculture  or  as  scavengers  has  been  more  generally 
recognized.  People  generally  have  begun  to  take  pleasure 
in  having  birds  about,  for  their  beauty  of  form,  or  color,  or 
movement,  and  for  their  song,  so  that  an  aesthetic  argument 
has  been  added  to  the  others.  The  separate  states  have 
shown  the  effect  of  this  general  awakening  by  the  improve- 
ment of  old  laws  or  the  passage  of  new  ones  for  the  protec- 
tion of  the  insectivorous  song-birds  and  other  birds  which 
have  not  been  proven  to  be  directly  injurious.  The  Audubon 
societies  of  the  country  and  the  Committee  on  Bird  Pro- 
tection of  the  American  Ornithologists  Union  were  helpful 
in  arousing  a  public  sentiment  which  made  possible  in  May, 
1900,  the  passage  by  the  federal  government  of  an  act  "to 


396 


GENERAL  ZOOLOGY 


aid  in  the  restoration  of  such  birds  in  those  parts  of  the 
United  States  adapted  thereto  where  the  same  have  become 
scarce  or  extinct,  and  also  to  regulate  the  introduction  of 
American  or  foreign  birds  or  animals  in  localities  where  they 
have  not  heretofore  existed."  By  its  provision  the  preserva- 
tion of  birds  is  placed  under  the  jurisdiction  of  the  Depart- 
ment of  Agriculture.  The  importation  of  foreign  wild  birds 
is  forbidden  without  permits  from  the  department,  and  in- 
terstate traffic  in  birds  killed  in  violation  of  state  laws  is 
prohibited.  This  is  the  most  sweeping  act  of  legislation  in 
favor  of  birds  ever  attempted,  and  it  is  confidently  expected 
to  give  them  a  great  measure  of  protection.  As  one  result  of 
the  interest  in  the  study  of  birds  in  the  schools  several  states 
have  set  apart  a  Bird  Day,  which  is  observed  after  the  fashion 

of  Arbor  Day,   and  oftentimes 
in  connection  with  it.    The  first 
Bird  Day  was  observed  in  Penn- 
\/>       m,    sylvania,  May  4,  1894. 

Geological  Development  of 
Birds.  The  earliest  remains  of 
birds  of  which  we  have  any 
knowledge  come  from  the  Age 
of  Reptiles.  The  oldest  of 
these  remains  is  the  famous 
fossil  known  as  Archwop'teryx 
(Fig.  209),  two  specimens  of 
which  have  been  found  in 
Bavaria.  The  ancestry  of  all  known  birds  is  therefore  to  be 
traced  back,  at  least  so  far  as  our  knowledge  goes,  to  these 
two  specimens.  Archseopteryx  was  a  land  bird  about  the  size 
of  a  crow,  probably  arboreal  in  its  habits,  though  not  neces- 
sarily a  good  flier.  It  had  true  feathers,  but  it  was  very 
different  from  the  birds  of  to-day  in  that  it  possessed  teeth 
and  a  long,  lizard-like  tail  of  about  twenty  vertebra*.  These 


FIG.  209.  Archseopteryx.   (After 
Pycraft) 


THE  ALLIES  OF  THE  PIGEON:   AVES          397 

last  characteristics  are  strikingly  reptilian,  and  such  considera- 
tions point  to  the  fact  that  the  birds  developed  from  the  rep- 
tiles. As  the  development  was  undoubtedly  gradual,  we  should 
expect  to  find  forms  possessing  the  characters  of  both  groups. 

Many  bird-remains  have  been  found,  especially  in  the  rocks 
on  the  eastern  slope  of  the  Rocky  Mountains,  in  Kansas  and 
Colorado,  which  belong  to  species  which  lived  later  in  the 
period.  These  birds  are  of  at  least  two  different  types,  dif- 
fering in  the  arrangement  of  the  teeth.  One  group  had  the 
teeth  set  in  separate  sockets ;  the  other  had  the  teeth  in 
grooves.  Some  of  the  birds  found  in  the  rocks  of  this  age 
in  New  Jersey  seem  to  have  been  toothless,  like  birds  to-day. 
It  is  interesting  to  note  that  even  thus  early  the  bird  type 
had  become  quite  well  advanced,  having  lost  not  only  the 
teeth  but  also  the  long  tail  of  earlier  forms.  The  time  of  this 
period  was  great  enough  to  permit  the  development  of  species 
of  birds  with  highly  developed  wings,  as  well  as  others  with 
degenerate  wings. 

In  the  next  succeeding  period,  to  which  we  shall  refer  at 
the  close  of  a  later  chapter,  the  birds  were  all  toothless  and 
related  to  those  of  to-day.  There  were  woodpeckers,  parrots, 
swallows,  cranes,  and  many  others. 


CHAPTER   XXX 
THE  GRAY  SQUIRREL 

Up  the  oak-tree,  close  beside  him, 
Sprang  the  squirrel,  Adjidaumo, 
In  and  out  among  the  branches 
Coughed  and  chattered  from  the  oak-tree. 

LONGFELLOW,  The  Song  of  Hiawatha. 

Habitat  and  Distribution.  The  gray  squirrel  (Sciu'rus  caro- 
linen'sis,  Fig.  210)  \vas  formerly  found  all  over  the  wooded 
region  of  the  eastern  United  States,  and  still  exists,  though 
in  much  diminished  numbers,  wherever  its  numerous  enemies 
permit.  It  does  not  extend  farther  west  than  Minnesota  and 
Wisconsin.  It  prefers  those  regions  where  hardwood  trees 
grow,  seldom  being  found  in  the  depths  of  coniferous  forests. 

External  Structure.  The  elongate  body  is  covered  with  a 
skin  bearing  soft  hair,  and  is  clearly  divisible  into  a  head, 
neck,  trunk,  and  tail.  There  are  four  appendages,  the  legs. 
The  fore  legs  are  used  in  grasping  objects  and  bringing  them 
up  to  the  mouth,  and  the  hind  legs  for  making  the  long  leaps 
so  characteristic  of  the  squirrel's  method  of  progression  in 
trees.  Both  pairs  of  legs  show  the  divisions  which  we  have 
already  noted  in  the  amphibians,  reptiles,  and  birds,  and  they 
are  provided  at  the  end  with  digits  ending  in  horny  claws. 
The  nostrils  (Fig.  213,  2)  are  situated  at  the  anterior  extrem- 
ity, just  above  the  mouth.  The  eyes  are  large,  and  furnished 
with  an  upper  and  lower  eyelid  and  a  nictitating  membrane. 
About  the  mouth  and  eyes  are  long,  sensitive  hairs  called 
vibrissce.  At  the  back  of  the  head  are  movable  flaps  of  skin 
(pinnw,  Fig.  213,  l),  placed  at  the  opening  of  the  ears.  The 
long  and  bushy  tail  is  useful  in  a  number  of  ways :  it  is  an 


THE  GRAY  SQUIRREL 


399 


ornament ;  it  is  useful  as  a  balancing  organ  in  the  long  leaps 
from  branch  to  branch ;  and  it  serves  to  keep  the  squirrel 
warm  in  its  nest  in  cold  weather. 

The  Digestive  System.    The  mouth  is  provided  with  fleshy 
lips,  which  assist  in  seizing  and  holding  food.    On  the  ventral 


FIG.  210.  Photograph  of  Gray  Squirrel 

surface  of  the  mouth  rests  a  large,  fleshy  tongue  (Fig.  213,  5), 
with  numerous  nerve-endings  of  the  organ  of  taste  (papillae) 
scattered  over  the  surface.  Two  kinds  of  teeth  are  present. 
The  front  teeth,  called  incisors  (Fig.  213,  4),  are  long,  sharp, 
and  chisel-shaped,  and  are  fitted  for  gnawing;  those  in  the 
back  of  the  jaw,  separated  from  the  incisors  by  quite  a  space, 


400  GENERAL  ZOOLOGY 

are  shorter,  broader,  and  flattened  on  top,  and  are  fitted  for 
grinding  (Fig.  211).  The  incisors  are  four  in  number,  two 
in  each  jaw;  the  grinding-teeth  in  an  adult  squirrel  may 

be  eighteen  in 
number,  --  four 
on  either  side 
of  the  lower  jaw 
and  five  on  either 
side  of  the  upper 
jaw.  Of  the 
grinding-teeth 
the  last  three 
on  either  side 
in  both  jaws  are 
termed  molars, 

the    others    pre- 
FIG.  211.  Skull  of  Squirrel  ,  ~  f 

molars.    One    01 

the  premolars  in  the  upper  jaw  is  very  likely  to  be  minute,  or 
even  missing,  having  been  shed  in  early  life.  The  complete 
dentition  can  be  expressed  in  a  simple  formula,  using  letters 
to  stand  for  the  names  of  the  teeth,  and  placing  the  lower 
jaw  below  the  line,  thus  : 

.2          4       6      12  . 

i-ipm'-am'6SBi6s 

or,  because  each  side  of  each  jaw  is  similar  to  the  other, 
.1          236 


A  tooth  contains  &  pulp-cavity  (Fig.  212,  4)  supplied  with 
blood-vessels  and  nerves,  and  surrounded  by  a  mass  of  firmer 
tissue,  or  dentine  (Fig.  212,  3),  which  makes  up  the  bulk  of  the 
tooth.  The  dentine  is  usually  covered,  where  the  tooth  pro- 
jects from  the  gum,  with  a  very  hard,  smooth  substance  called 


THE  GRAY  SQUIRREL 


401 


enamel  (Fig.  212,  l) ;  below  there  is  a  bony  substance,  the 
cement  (Fig.  212,  2),  surrounding  the  root  of  the  tooth.  In 
the  molar  teeth  of  the  squirrel  the  pulp-cavity,  which  is  at 
first  open  at  the  base,  as  in  the  case  of  man  (shown  in  Fig. 
212,  B),  becomes  inclosed  and  develops  a  root  (see  Fig.  212,  C), 
after  which  all  growth  of  the 
tooth  stops.  In  the  incisors 
of  the  squirrel  the  pulp-cav- 
ity persists  throughout  life, 
remaining  open  so  that  the 
tooth  continues  to  grow  as 
fast  as  it  is  worn  away.  The 
enamel  is  confined  to  the 
front  surface  of  the  incisors, 
so  that  when  the  tooth  is 
used  on  hard  substances  the 
softer  dentine  wears  away 
more  quickly  and  the  tooth 
becomes  sharper  the  more  it 
is  used. 

In  most  fur-bearing  animals 
the  lower  jaw  is  articulated  to 
the  upper  by  means  of  trans- 
verse condyles,  but  in  the 
squirrel  and  its  allies  the 
condyles  are  parallel  with 
the  long  diameter  of  the  head, 
thus  allowing  some  backward  (From  Flower  and  Lydekker's  Mammals) 
and  forward  motion  of  the 

lower  jaw.  The  advantages  of  these  special  adaptations  of 
the  structure  of  teeth  and  jaws  to  the  life  of  a  gnawing 
animal  like  the  squirrel  are  obvious. 

The  ducts  of  four  pairs  of  salivary  glands  open  into  the 
mouth.    A  muscular  flap,  called  the  soft  palate,  to  distinguish 


D 


FIG.  212.   Sections  of  Teeth 

incisor  or  tusk  of  elephant ;  .B, 
human  incisor  during  development; 
C,  human  incisor  completely 
formed  ;  D,  human  molar;  E,  molar 
of  ox  ;  1,  enamel ;  2,  cement;  3,  den- 
tine ;  4,  pulp-cavity 


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402 


THE  GRAY  SQUIRREL  403 

it  from  the  roof  of  the  mouth,  or  hard  palate,  separates  the 
mouth  from  the  pharynx  (Fig.  213,  6).  Imbedded  in  the  soft 
tissues  of  the  soft  palate  are  the  tonsils,  two  small  oval  bodies 
the  function  of  which  is  unknown.  The  nostrils  open  pos- 
teriorly (Fig.  213,  3)  into  the  pharynx.  The  Eustachian  tubes 
from  the  ears  enter  the  pharynx  at  the  sides. 

A  short,  straight  oesophagus  (Fig.  213,  7,  8)  leads  to  the 
sac-like  stomach  (Fig.  213,  9),  passing  through  a  muscular 
partition  called  the  diaphragm  (Fig.  213,  19),  which  separates 
the  heart  and  lungs  in  the  thoracic  cavity  from  the  organs 
of  the  abdominal  cavity.  In  the  first 
fold  of  the  intestine  is  the  pancreas 
(Fig.  213,  13),  an  extended  mass  of 
spongy  tissue  roughly  suggesting  a 
bunch  of  grapes.  The  liver  (Fig. 
213,  11)  is  large  and  is  divided  into 
several  lobes.  The  intestine  is  very 
long  and  much  coiled.  A  clearly 
marked  anterior  portion,  the  small 
intestine  (Fig.  213,  10),  can  be  distin- 
guished from  the  posterior  portion,  or  FlG-  214-  Caecum  and  Ver- 
rectum  (Fig.  213, 14).  At  the  junction  miform  APPeildix  of  the 

.   , ,  °n    .    ,      /.  .          Squirrel 

of  the  small  intestine  and  rectum  is 

the  cwcum  (Fig.  214),  from  which  projects  a  closed  finger-like 
appendix  vermiformis. 

Ductless  Glands.  Several  glands,  called  ductless  glands 
(owing  to  the  absence  of  a  duct  leading  from  them),  are 
present  in  vertebrates.  With  the  single  exception  of  the 
spleen  (mentioned  in  each  case  in  the  course  of  the  statements 
concerning  the  digestive  system)  they  have  not  been  referred 
to  in  our  brief  discussion  of  the  internal  anatomy  of  the 
classes  of  vertebrates,  but  as  they  show  plainly  in  the  squirrel, 
attention  may  be  called  to  them  at  this  time.  They  are, 
besides  the  spleen  (Fig.  213, 15),  the  adrenal  capsules  (Fig.  213, 16), 


404  GENERAL  ZOOLOGY 

just  anterior  to  the  kidneys,  the  thymus  (Fig.  213,  17),  and  the 
thyroid  gland  (Fig.  213,  18).  Their  functions  are  not  thor- 
oughly understood. 

The  Circulatory,  Respiratory,  and  Excretory  Systems.  The 
heart  is  inclosed  in  a  pericardium  (Fig.  213,  20),  and  is  of  the 
four-chambered  type  found  in  the  birds.  There  is  a  complete 
double  circulation  of  the  blood  in  the  squirrel,  as  in  birds. 
The  lymphatic  vessels  of  the  abdomen,  called  lacteals,  which 
carry  from  the  intestine  the  absorbed  fatty  materials  of  food, 
unite  to  form  a  thoracic  duct,  which  extends  anteriorly  and 
empties  into  the  venous  system  near  the  heart. 

At  the  anterior  end  of  the  larynx  is  a  cartilaginous  flap 
called  the  epiglottis  (Fig.  213,  30).  The  lungs  (Fig.  213,  32) 
are  larger  and  more  extensible  than  in  the  birds,  and  hang 
free  in  the  thoracic  cavity.  Respiration  is  effected  mainly  by 
movements  of  the  diaphragm  and  the  ribs,  thus  altering  the 
size  of  the  thoracic  cavity  and  causing  air  to  enter  and  to 
leave  the  lungs. 

The  kidneys  (Fig.  21.3,  33)  are  almond-shaped  bodies  in  the 
dorsal  part  of  the  abdominal  cavity.  The  ureters  (Fig.  213,  34) 
lead  from  them  to  the  urinary  bladder  (Fig.  213,  35),  whence 
the  waste  products  are  carried  to  the  surface  by  the  urethra 

(Fig.  213,  36,  37). 

The  Skeletal  System.  The  skeleton  is,  in  general,  built 
upon  the  plan  with  which  we  have  become  familiar  in  the 
study  of  the  frog,  the  lizard,  and  the  pigeon.  The  cranium 
(Fig.  213,  38)  is  articulated  to  the  vertebra  by  two  condyles, 
as  in  the  amphibians.  All  the  vertebra  (Fig.  213,  40),  except 
those  in  the  pelvic  region,  are  free. 

The  Nervous  and  Muscular  Systems.  The  nervous  system 
is  similar  to  that  of  the  bird,  but  the  cerebrum  (Fig.  213,  44) 
is  considerably  more  differentiated.  The  muscles,  especially 
those  in  the  hind  legs,  form  a  complex  system  adapted  to 
strong  and  rapid  movement. 


THE  GRAY  SQUIRREL  405 

The  Reproductive  System.  The  organs  of  reproduction  in 
the  male  consist  of  oval  spermaries  (Fig.  213,  48)  and  &  penis 
(Fig.  213,  54) ;  in  the  female,  of  ovaries  with  their  oviducts. 

Development.  The  squirrel  is  viviparous.  The  ovum  pro- 
duced in  the  ovary  passes  into  the  oviduct,  where  it  becomes 
fertilized,  and  in  that  portion  of  the  oviduct  called  the  uterus 
it  develops  into  the  young  squirrel.  The  young  is  born  in  a 
condition  resembling  the  adult,  though  the  hair  is  not  com- 
letely  formed  and  the  eyes  are  closed.  In  the  southern  states 
the  first  of  two  or  three  litters  appears  early  in  March,  and 
four  young  are  usually  produced  at  a  birth.  The  nest  is 
usually  in  a  hollow  tree  in  the  colder  portions  of  its  range, 
and  exposed  on  the  branches  in  the  warmer  regions.  The 
female  keeps  the  male  away  from  the  young  during  their 
period  of  infancy,  and  feeds  them  on  milk,  which  is  secreted 
by  the  mammary  glands  on  her  ventral  surface. 

Relation  to  Environment.  When  the  young  have  been 
reared,  the  winter  nest  in  a  hollow  tree  is  usually  deserted 
for  a  structure  of  leaves  and  twigs  built  high  among  the 
branches  of  a  tree.  This  outside  nest  is  occupied  (at  least  in 
the  colder  regions)  throughout  the  summer. 

The  food  of  the  squirrel  in  the  spring  consists  largely  of 
buds,  especially  of  the  maple  and  elm.  In  the  summer,  fungi 
and  berries  are  added  to  the  bill  of  fare,  and  in  the  fall  nuts 
form  a  large  part  of  the  diet.  The  gray  squirrel  has  been 
accused  of  varying  its  vegetable  diet  with  such  animal  food 
as  the  young  and  the  eggs  of  song-birds,  but  it  is  probably 
not  as  frequent  an  offender  as  the  red  squirrel,  whose  bad 
habits  in  this  respect  are  well  known.  The  nuts  of  autumn 
are  gathered  and  stored  in  secret  places  beneath  stumps  and 
in  hollow  trees,  and  many  are  separately  buried  in  the  ground. 
Some  observers  are  inclined  to  think  that  their  sense  of  smell 
guides  them  to  the  buried  food,  though  it  is  doubtful  if  these 
individual  hoards  are  always  located  again. 


406  GENERAL  ZOOLOGY 

When  winter  comes  on,  gray  squirrels  are  likely  to  be 
later  in  rising  in  the  morning,  preferring  to  come  out  in  the 
warmest  part  of  the  day,  and  on  some  inclement  days  they 
may  not  venture  forth  at  all.  There  is  no  evidence,  however, 
that  they  truly  hibernate. 

Gray  squirrels  have  been  known  to  travel  in  bands  from 
place  to  place.  Of  late  years,  either  on  account  of  their 
much  diminished  numbers  or  because  of  change  in  the  food- 
supply,  we  see  little  of  the  great  migrations  which  formerly 
occurred.  Many  such  visitations  have  been  recorded.  Penn- 
sylvania was  overrun  with  squirrels  in  1749,  and  a  bounty  of 
threepence  a  head  was  offered  for  their  destruction.  It  is 
estimated  that  about  six  hundred  and  forty  thousand  squirrels 
were  killed  at  that  time.  In  their  migrations  bodies  of  water 
were  crossed  by  swimming,  though  ordinarily  squirrels  are 
not  lovers  of  water.  The  cause  of  the  migrations  is  probably 
to  be  looked  for  in  connection  with  the  scarcity  of  the  food- 
supply. 

The  general  color  of  .the  gray  squirrel's  fur  is  protective, 
and  the  animal  has  the  habit  of  flattening  itself  on  the  upper 
side  of  a  horizontal  branch,  so  that  it  is  invisible  from  below. 
Of  their  enemies,  the  hawks  probably  give  them  most  trouble. 
It  is  said  that  the  red-tailed  hawks  hunt  them  in  pairs,  thus 
making  futile  their  habit  of  dodging  to  the  far  side  of  a 
branch. 

Spread  over  a  large  area  from  Maine  to  Minnesota  and 
south  as  far  as  Florida,  it  is  to  be  expected  that  the  different 
individuals  will  vary  considerably.  In  general,  it  is  found 
that  the  colors  increase  in  intensity  southward  and  in  regions 
of  copious  rainfall,  while  the  legs,  tail,  and  ears  show  a  tend- 
ency to  increase  in  length.  In  all  parts  of  their  range  indi- 
viduals are  sometimes  born  in  which  the  normal  coloring- 
matter  of  the  hairs  is  replaced  by  black  pigment,  and  others 
in  which  the  pigment  is  lacking,  leaving  the  fur  white. 


THE  GRAY  SQUIRREL  407 

The  black  individuals  are  examples  of  melanism;  the  white, 
of  albinism.  Both  conditions  are  quite  common  among 
squirrels. 

The  calls  of  the  gray  squirrels  to  each  other  may  often  be 
.heard  in  the  woods,  especially  in  the  fall.  The  "  barking,"  as 
it  is  termed,  consists  of  a  series  of  notes  ending  in  a  longer 
snarl.  It  expresses  anger,  alarm,  or  warning.  Gray  squirrels 
have  sometimes  been  encouraged  to  make  their  homes  in  city 
parks,  where  they  soon  learn  to  accept  and  finally  to  be 
largely  dependent  on  contributions  of  food  from  human 
visitors. 


CHAPTER  XXXI 
THE  ALLIES  OF  THE  SQUIRREL :  MAMMALIA 

They  say, 

The  solid  earth  whereon  we  tread 
In  tracts  of  fluent  heat  began, 

And  grew  to  seeming  random  forms, 
The  seeming  prey  of  cyclic  storms, 
Till  at  the  last  arose  the  man. 

TENNYSON,  In  Memoriam. 

Definition  of  Mammalia  (Lat.  mamma,  breast).  The  squir- 
rel serves  to  introduce  the  Mamma'lia,  the  highest  class  of 
the  animal  kingdom.  Mammals  are  warm-blooded  verte- 
brates covered  with  hair.  Generally  two  pairs  of  appendages 
are  present,  the  anterior  of  which  are  never  absent  in  any 
member  of  the  class.  Mammals  breathe  by  lungs.  Teeth  are 
almost  invariably  present,  in  the  majority  of  cases  occurring 
in  two  sets.  Mammals  bring  forth  their  young  alive  and  feed 
them  on  milk,  except  in  the  very  few  cases  to  be  referred  to 
under  the  Monotremata  below. 

The  principal  orders  into  which  the  class  is  divided  are 
mentioned  in  the  following  pages. 

The  Duckbill  and  Allies.  The  duckbill  (OrnitJiorJiyn' chus 
anati'nm,  Fig.  215)  and  two  or  three  species  of  spiny  ant- 
eater  (Echid'na),  mammals  of  the  size  of  a  rabbit  and  found 
only  in  Australia,  Tasmania,  and  New  Guinea,  have  many 
special  characteristics.  The  name  Monotrem'ata  is  given  to 
them  in  reference  to  the  fact  that  these  mammals  possess  but 
a  single  opening  (cloaca)  through  which  the  contents  of  the 
intestine  and  the  urinary  and  reproductive  products  pass 
outward,  as  in  the  case  of  amphibians,  birds,  and  reptiles. 
Monotremes  also  stand  alone  among  mammals  in  the  fact 

408 


THE  ALLIES  OF  THE  SQUIRREL:  MAMMALIA     409 

that  they  lay  eggs  inclosed  in  a  white,  flexible  shell,  remind- 
ing one  of  the  egg  of  a  reptile.  The  duckbill  gets  its  name 
from  its  peculiar  duck-like  beak,  which  is  toothless  when  the 
animal  is  full  grown,  the  teeth  being  shed  after  they  have 
been  used  for  a  while.  The  male  has  a  hollow  spur  on  the 
heel,  which  is  connected  with  a  poison-gland  in  the  thigh. 
The  duckbill  is  semiaquatic,  and  lives  in  burrows  in  the 


FIG.  215.  Duckbill 
(From  Lydekker's  Geographical  History  of  Mammals) 

banks  of  ponds  and  streams.  Its  food  consists  of  mollusks, 
small  insects,  worms,  and  crustaceans.  Spiny  ant-eaters  are 
inhabitants  of  elevated  rocky  districts  and  feed  on  ants. 
They  are  protected  by  a  covering  of  spines  intermixed  with 
the  hairs. 

Kangaroos,  Opossums,  and  Allies.  The  order  Marsupia'lia 
(Lat.  marsupium,  a  pouch)  contains  a  large  number  of  spe- 
cies, almost  all  of  which  are  confined  to  Australia  and  the 


410 


GENERAL  ZOOLOGY 


surrounding  islands.  The  mammals  comprising  it  are  of  vari- 
ous external  form,  but  the  females  of  nearly  all  species  have 
an  abdominal  fold  of  skin  forming  a  pouch  into  which  the 
almost  helpless  young  are  placed  by  the  mother  when  born  ; 
they  are  then  carried  about  with  her  until  they  are  able  to 
take  care  of  themselves.  The  kangaroos  vary  from  the  size 
of  a  rabbit  to  that  of  a  sheep.  The  hind  legs  are  developed 
for  jumping.  The  Virginian  opossum  (Didel'pJiys  Virginia 'na, 


FIG.  210.  Photograph  of  Opossum 

Fig.  216)  of  our  southern  and  middle  Atlantic  states  is  the 
most  northern  member  of  the  opossum  group,  many  species  of 
which  are  found  in  South  and  Central  America.  It  has  the 
habit  of  feigning  death  when  in  danger 'of  capture,  hence  the 
expression,  "  playing  'possum." 

Fossils  from  the  rocks  of  the  latter  part  of  the  Age  of  Rep- 
tiles show  that  marsupials  were  widely  distributed  over  the 
earth  at  that  time.  Then  came  the  separation  of  the  Austra- 
lian continent  from  the  land  to  the  north,  isolating  the  mar- 
supial fauna  from  the  larger  and  more  diversified  land  areas. 


THE  ALLIES  OF  THE  SQUIRREL:  MAMMALIA     411 

The  Australian  fauna  evolved  along  various  lines,  produ- 
cing herbivorous,  insectivorous,  and  carnivorous  forms  which 
resemble  in  outward  appearance  the  members  of  the  higher 
orders,  though  they  are  in  reality  marsupial  in  structure. 
Over,  the  rest  of  the  world,  witli  the  exception  of  America, 
the  marsupials  were  entirely  destroyed  and  their  places  taken 
by  more  highly  specialized  types.  Marsupials  retained  a  foot- 
hold in  South  America  owing  to  the  absence  of  overpowering 
enemies,  and  on  account  of  their  adaptation  to  climatic  and 


FIG.  217.   Photograph  of  Armadillo 

general  environmental  conditions.  They  afford  an  illustration 
of  discontinuous  distribution. 

Sloths,  Armadillos,  and  Allies.  Both  terrestrial  and  arboreal 
animals  are  included  in  the  order  Edenta'ta  (Lat.  e,  out;  dens, 
tooth).  Edentates  have  incompletely  developed  teeth,  or  if 
the  teeth  are  well  developed,  they  are  of  simple  structure; 
true  incisors  are  never  present.  Many  members  of  the  order 
have  a  covering  of  scales  formed  from  the  hardening  of  the 
skin. 

The  armadillos  (Fig.  217)  are  terrestrial  American  forms 
which  are  protected  by  the  scaly  covering  just  referred  to. 
The  tail  and  head  are  generally  exposed,  but  the  animals  can 


412  GENERAL  ZOOLOGY 

roll  themselves  into  a  ball,  thus  offering  a  hard  surface  in 
every  direction. 

The  sloths  of  South  and  Central  America  are  nocturnal, 
arboreal  animals;  their  natural  attitude  during  the  day  is 
hanging  from  a  branch  back  downward.  The  hair  is  gray, 
but  in  some  species  it  offers  a  lodgment  for  a  green  alga,  a 
plant  of  low  organization,  which  gives  the  hair  a  green  tinge 
like  that  of  the  masses  of  vegetation  of  the  tropical  forest. 
Sloths  rarely  descend  from  the  branches  of  trees. 

Whales,  Dolphins,  Porpoises,  and  Allies.  The  whales,  dol- 
phins, and  porpoises  are  true  mammals,  though  so  adapted 
to  their  aquatic  life  that  they  seem,  on  superficial  examina- 
tion, to  be  fishes.  The  name  of  the  order,  Ceta'cea,  is  derived 
from  the  Latin  cetus,  a  whale. 

Flower  and  Lydekker,  in  their  Mammals,  thus  review  the 
principal  peculiarities  of  the  group :  "  The  external  fish-like 
form  is  perfectly  suited  for  swimming  through  the  water  ; 
the  tail,  however,  is  not  placed  vertically  as  in  fishes,  but 
horizontally,  a  position  which  accords  better  with  the  con- 
stant necessity  for  rising  to  the  surface  for  the  purpose  of 
breathing.  The  hairy  covering  characteristic  of  all  mammals, 
which,  if  present,  might  interfere  with  rapidity  of  movement 
through  the  water,  is  reduced  to  the  merest  rudiments,  —  a  few 
short  bristles  about  the  chin  or  upper  lip,  —  which  are  often 
present  only  in  very  young  animals ;  and  the  function  of 
keeping  the  body  warm  is  performed  by  the  '  blubber.'  The 
fore  limbs,  though  functionally  reduced  to  mere  paddles, 
with  no  power  of  motion  except  at  the  shoulder-joint,  have 
beneath  their  smooth  and  continuous  covering  all  the  bones, 
joints,  and  even  most  of  the  muscles,  nerves,  and  arteries  of 
the  human  arm  and  hand ;  the  rudiments  of  hind  legs,  found 
buried  deep  in  the  interior  of  the  animal,  apparently  sub- 
serve no  useful  purpose,  but  point  an  instructive  lesson  to 
those  who  are  able  to  read  it." 


OF  THf 

UNIVERSITY 

THE  ALLIES  OS\THE  SQUIRR^t:  MAMMALIA    413 


Cetaceans  are  found  in  al  seas,  and  feed  on  fishes,  crus- 
taceans, and  the  smaller  floating  animal  life  of  the  ocean  gen- 
erally. They  vary  from  four  to  eighty  feet  in  length,  some 
of  the  whales  being  the  largest  of  existing  animals.  There  is 
every  reason  to  believe  that  the  group  is  descended  from  land- 
mammals.  The  whalebone-whales  are  species  without  teeth, 
but  with  a  development  of  baleen  or  whalebone  in  the  upper 
jaw,  which  acts  as  a  strainer.  By  means  of  the  closely  set, 
flexible  strips  of  whalebone  the  small  animals  on  which  they 
feed  are  retained,  while  the  water  is  forced  out.  Several 
species  are  found  in  the  Atlantic  and  Pacific  oceans.  The 
sperm-whale  (Physe'ter  macroceph' alus)  has  a  square  head, 


FIG.  218.  Narwhal.    (After  Cuvier) 

within  which  is  a  cavity  containing  oil,  which  on  being  refined 
yields  spermaceti.  The  narwhal  (Mon'odon  monoc'eros,  Fig.  218) 
is  a  smaller  species,  the  males  of  which  possess  a  single  abnor- 
mally developed  incisor  tooth,  usually  on  the  left  side,  which 
grows  into  a  tusk  six  or  eight  feet  in  length. 

Hoofed  Mammals.  The  great  assemblage  of  animals  called 
Ungula'ta  (Lat.  unguis,  a  nail)  includes  the  hippopotami, 
pigs,  camels,  deer,  the  giraffes,  antelopes,  oxen,  goats,  sheep, 
rhinoceroses,  horses,  and  elephants.  All  these  mammals  have 
the  toes  ending  in  either  a  blunt  nail  or  a  fully  developed 
hoof,  both  of  which  structures  are  formed  from  the  thicken- 
ing of  the  skin  of  the  toes.  In  ungulates  like  the  cow  and 
sheep  there  are  two  divisions  in  the  hoof,  and  the  animals 
really  walk  on  the  tip  of  the  third  and  fourth  digits,  the  others 
being  much  reduced  in  size.  In  the  horse  and  its  allies  this 
reduction  has  gone  much  farther,  so  that  the  tip  only  of  the 


414  GENERAL  ZOOLOGY 

third  digit  is  used  for  support.  The  elephants  have  five  toes, 
each  incased  in  a  short  nail.  The  two  living  species  of  ele- 
phants would  undoubtedly  be  removed  to  a  separate  order  if 

fossil  forms  had  not  been 
discovered  possessing 
characters  intermediate 
between  these  mammals 
and  other  ungulates. 

Ungulates  are  adapted 
to  a  terrestrial  life  and 
feed  almost  entirely  on 
vegetable  food.  Four 
kinds  of  teeth  are  pres- 
FIG.  219.  Skull  of  Peccary,  showing  teeth  ^  __  incisors>  canines, 

premolars,  and  molars.  The  first  kind  and  the  last  two  kinds 
will  be  recognized  from  the  study  of  the  squirrel;  the  canines, 
so  named  because  they  are  well -developed  in  the  dog  (Lat. 
cam's,  a  dog),  fill  the  space  between  the  incisors  and  premolars. 
The  canines  are  often  elongated  to  form  tusks  for  defense  or 
for  obtaining  food  (see  Fig.  219) ;  the  incisors  serve  to  crop 
the  herbage  ;  the  molars  and  premolars  are  flattened  for 
grinding. 

Horns  for  defense  have  been  developed  in  many  species 
of  ungulates.  They  are  of  various  sorts.  The  rhinoceroses 
(Fig.  220)  have  one  or  more  median  horns,  which  are  com- 
posed of  a  thickened  and  hardened  portion  of  the  skin  and 
hair,  covering  a  short  protuberance  of  the  skull.  In  the 
giraffes  there  are  one  or  two  pairs  of  horns  consisting  of  a 
layer  of  skin  over  bony  processes  of  the  skull.  Neither  in 
the  rhinoceros  nor  the  giraffe  are  the  horns  ever  shed.  In  the 
North  American  pronghorn  antelope  (Antiloca'pra  america'na) 
the  horns  are  branched  and  consist  of  a  hardened  and  thick- 
ened skin  on  a  bony  core.  The  thickened  skin  is  shed  peri- 
odically but  the  core  is  retained.  The  horns  in  true  antelopes 


THE  ALLIES  OF  THE  SQUIRREL :  MAMMALIA     415 

and  in  oxen,  sheep,  and  goats,  are  of  similar  structure.  They 
are  usually  found  in  both  sexes  and  are  never  shed.  In  the 
deer  family  (Fig.  221)  the  horns,  called  antlers,  consist  of 
outgrowths  of  bone  covered  each  year  during  the  period  of 
growth  with  a  sensitive  skin  called  "  the  velvet."  When 
the  annual  growth  is  completed  the  supply  of  blood  to  the 
antlers  ceases  and  the  velvet  peels  off,  leaving  the  bone  bare. 
After  a  time  the  antlers  separate  from  the  skull  and  are  shed. 
In  most  deer  this  takes  place  annually.  In  some  members  of 
the  family  the  antlers  remain  simple  throughout  life ;  in 


Fi<;.  220.  Head  of  Rhinoceros 
(American  Museum  of  Natural  History) 

others  they  become  much  branched  in  successive  annual 
growths  (Fig.  221).  It  is  interesting  to  note  that,  in  a  broad 
way,  this  was  the  order  of  development  of  antlers  in  geo- 
logical time,  the  earliest  deer  of  which  we  have  any  knowl- 
edge being  without  them.  Horns  and  antlers  are  used  in  the 
battles  of  the  males  for  the  possession  of  the  females,  as  well 
as  for  defense  of  themselves  and  their  band.  The  presence 


416 


GENERAL  ZOOLOGY 


FIG.  221.  Series  of  Antlers 

(American  Museum  of  Natural 
History) 


of  these  organs  is  usually  ascribed 
to  the  action  of  sexual  selection. 

A  large  number  of  the  ungulates 
have  learned  the  advantage  of 
cooperation,  and  live  in  herds,  which 
possess  an  organized  power  of  resist- 
ance far  greater  than  any  individual 
has.  In  many  cases,  especially  among 
the  deer,  scent-glands  are  developed 
on  the  head  below  the  eyes,  and  as 
the  sense  of  smell  is  extremely  acute, 
notice  of  the  presence  of  other  mem- 
bers of  the  herd  is  given  by  the  odor 
of  the  secretion  from  these  glands. 
Often  the  tail  and  rump  are  con- 
spicuously marked  with  white,  show- 
ing plainly  when  the  animal  is  in 
flight,  and  probably  serving  as  a 
recognition  or  signaling  mark. 

The  structural  peculiarities 
already  referred  to  form  the  basis  for 
separating  the  ungulates  into  three 
divisions, — those  with  an  even  num- 
ber of  toes,  as  the  cow ;  those  with 
an  odd  number  of  toes  (one  or  three), 
as  the  rhinoceros  and  horse ;  and 
the  long-nosed  forms  (Proboscid'ea), 
including  the  elephants.  Of  the 
even-toed  ungulates  the  families  of 
camels  (Camel'idce),  deer  (Cer'vidce) 
and  antelopes,  goats,  sheep,  and 
oxen  (Bo'vidw),  have  the  stomach 
(Fig.  222)  divided  into  a  digestive 
and  a  non-digestive  or  storage  region, 


THE  ALLIES  OF  THE  SQUIRREL:  MAMMALIA     417 


forming  a  complex  organ  of  several  compartments.  The  food 
is  taken  into  the  first  two  of  these  divisions,  the  reticulum  or 
honeycomb  bag,  and  the  rumen  or  paunch,  where  it  remains 
till  the  animal  has  finished  grazing  and  has  leisure  for  its 
digestion.  The  food  is  then  raised  to  the  mouth  in  a  some- 
what softened  condition  and  is  there  ground  between  the 
molar  teeth  and  moistened  with  saliva,  after  which  it  is  again 
swallowed,  this  time  into  the  psalterium,  or  manyplies,  so 
called  from  the  numerous  folds  in  its  lining  membrane.  The 
food  slowly  filters  through  the 
manyplies  into  the  true  digestive 
stomach,  or  abomasum.  This  habit 
of  chewing  the  cud  has  suggested 
the  name  of 
ruminants  (Lat. 
rumen,  throat) 
for  these  ungu- 
lates. 

Though  zoolo- 
gists do  not  feel 
certain  as  to  the 
ancestry  of  the 
domestic  horse 
(E'quus  cabal'lus),  a  recently  discovered  animal  (Equus 
przewal'skii,  Fig.  223)  of  the  sandy  deserts  of  Central  Asia 
may  be  its  progenitor.  The  interesting  story  of  the  geological 
development  of  the  horse  is  told  farther  on  (p.  428). 

Of  the  Proboscidea  the  elephants  alone  require  mention. 
There  are  two  existing  species,  the  Asiatic  (El'ephas  in'di- 
cus)  and  the  African  elephant  (Elephas  africa'nus).  The  latter 
can  be  distinguished  from  the  former  by  its  very  large  ears. 
The  Asiatic  species  has  long  been  domesticated  and  many 
stories  are  told  of  its  intelligence.  The  African  species 
was  used  by  the  Romans  in  battle  and  circus  games,  but  in 


FIG.  222.  Diagram  of  Stomach  of  Ruminant.    (After 

Wiedersheim) 
(Arrows  and  dotted  lines  show  the  course  of  the  food) 


418 


GENERAL  ZOOLOGY 


modern  times  these  animals  have  been  hunted  so  persist- 
ently for  their  ivory  that  there  is  danger  of  their  being  ex- 
terminated. Steps  are  now  being  taken  to  prevent  their 
complete  destruction. 

Gnawing  Mammals.  The  Roden'tia  (Lat.  rodere,  to  gnaw) 
are  the  most  numerous  in  point  of  species  and  are  the  most 
widely  distributed  of  all  the  mammals.  Here  belong  the 


FIG.  223.  Photograph  of  Frzewalsky's  Horse 

hares,  guinea-pigs,  porcupines,  mice,  rats,  beaver,  woodchuck, 
prairie-dog,  and  squirrels.  Rodents  are  distinguished  by  the 
absence  of  canine  teeth  and  the  presence  of  chisel-shaped 
incisors,  which  grow  from  persistent  pulps  (see  Fig.  212). 
They  are  mostly  terrestrial  animals,  though  a  few,  like  the 
beaver,  are  modified  for  an  aquatic  existence,  and  others,  like 
the  squirrels,  for  life  in  the  trees. 

The  hares  are  distinguished  from  all  other  rodents  by  the 
presence  of  a  second  pair  of  incisor  teeth  behind  the  first  pair 


THE  ALLIES  OF  THE  SQUIRREL:  MAMMALIA     419 

in  the  upper  jaw.  Well-known  American  species  are  the 
cottontail,  or  gray  rabbit,  of  the  East  (Le'pus  florida'nus),  the 
varying  hare  (Lepus  america'nus)  of  the  North,  and  the  north- 
ern jack-rabbit  (Lepus  campes'tris)  of  the  West.  The  cottontail 
is  so  named  from  the  white  tail,  which  is  plainly  shown  in 
flight  and  probably  serves  as  a  signaling  or  recognition  mark. 
The  varying  hare  is  a  larger  and  more  northern  species  which 
takes  on  a  white  coat  of  fur  in  winter.  The  northern  jack- 
rabbit  also  changes  to  white  in  the  northern  part  of  its  range ; 
farther  south  the  change  is  only  partial  or  entirely  wanting. 
The  domestic  rabbit  is  descended  from  the  common  rabbit  of 
the  Mediterranean  basin  (Lepus  cunic'ulus). 

The  porcupine  (Erethi'zon  dorsa'tus)  is  a  sluggish,  stupid 
animal,  which,  having  spines  for  protection,  relies  on  them 
to  such  an  extent  that  it  hunts  its  food  in  the  daytime,  — 
a  habit  which  most  rodents  have  had  to  give  up  (if  they 
ever  possessed  it)  on  account  of  their  lack  of  protection  and 
means  of  defense  against  numerous  enemies.  The  squirrels 
have  solved  the  problem  in  another  way  by  the  development 
of  extreme  watchfulness.  There  is  no  truth  in  the  oft- 
repeated  statement  that  the  porcupine  can  shoot  its  quills, 
the  fact  being  that,  as  they  are  loosely  attached,  they  are 
likely  to  come  out  on  slight  pressure. 

So  much  has  been  written  on  the  beaver  and  its  works 
that  its  habit  of  felling  trees  for  its  dam  or  for  food,  its  win- 
ter storage  of  branches  or  twigs  beneath  the  ice,  and  the 
habits  developed  in  connection  with  its  communal  life  are 
pretty  well  known  to  everybody.  In  the  communal  life  of 
the  beaver,  as  among  the  bees  and  wasps,  instinctive  actions 
are  performed  with  a  high  degree  of  perfection.  The  beaver 
also  has  capabilities  of  meeting  new  conditions,  and  it  has 
been  credited  with  a  considerable  degree  of  intelligence. 
It  has  been  hunted  so  persistently  for  its  fur  and  scent- 
bags  that  it  is  now  almost  extinct.  The  few  remaining 


420  GENERAL  ZOOLOGY 

individuals  scattered  in  isolated  colonies  seldom  dare  to  raise 
lodges,  but  have  to  be  content  with  a  home  in  the  bank  of 
some  stream. 

Flesh-Eating  Mammals.  The  carnivorous  mammals,  Car- 
niv'ora  (Lat.  caro,  flesh ;  vorare,  to  devour),  are  the  flesh-eaters 
par  excellence.  The  incisor  teeth  are  small  and  sharp ;  the 
canines  are  generally  long,  strong,  and  conical,  fitted  for 
tearing ;  and  the  pre molars  and  molars  are  raised  into  more 
or  less  sharp  ridges.  The  toes  are  sheathed  in  claws,  often 
fitted  for  grasping,  and  in  one  family,  the  cats,  are  capable 
of  being  retracted  and  thus  kept  sharp  by  being  saved  from 
constant  friction.  The  group  has  divided  along  two  main 
lines  of  development,  one  adapted  to  terrestrial,  the  other  to 
aquatic  life.  To  the  first  belong  the  family  of  cats  (Fe'lidoe), 
including  the  lion,  tiger,  leopard,  lynx,  jaguar,  and  puma  ; 
the  hyenas  (Hycen'idce) ;  the  dogs,  wolves,  and  foxes  ( Oan'- 
idov)'9  the  bears  ( Ur'sidcc) ;  and  the  raccoons  (Procyon'idce). 
To  the  second  division  belong  the  seals  and  walruses. 

The  jaguar  is  a  South  American  cat  resembling  in  general 
appearance  the  leopard  of  Africa,  and,  like  it,  an  inhabitant 
of  wooded  regions,  where  it  spends  much  of  its  time  in  trees. 
The  irregular  markings  resemble  in  a  general  way  the  pat- 
terns of  light  and  shade  beneath  the  leaves  of  a  forest.  The 
markings  are  usually  spoken  of  as  an  illustration  of  aggres- 
sive resemblance.  The  dun-colored  lion  and  the  gayly  striped 
tiger  are  mentioned  as  similar  examples,  the  one  resembling 
the  brown  of  desert  places  and  the  other  the  vertical  shadows 
of  reeds  and  grasses  in  tropical  jungles.  The  origin  of  our 
domestic  cat  and  dog,  like  that  of  some  of  our  other  domestic 
animals,  is  uncertain,  but  it  is  generally  believed  that  the  cat 
is  descended  from  the  Egyptian  or  Caff  re  cat  (Fe'lis  caf'frd}, 
an  African  and  Asiatic  species  domesticated  by  the  Egyptians 
and  held  in  veneration  by  them  ;  the  dog  is  variously  thought 
to  be  the  descendant  of  some  wild  species  now  extinct,  or  of 


THE  ALLIES  OF  THE  SQUIRREL:  MAMMALIA     421 

one  of  several  wolves  or  jackals,  or  a  mixture  of  several 
species.  The  great  length  of  time  since  the  dog  first  became 
the  companion  of  man,  and  the  numerous  races  which  have 
arisen,  render  the  question  extremely  complicated. 

Of  our  smaller  wild  carnivores  none  is  more  generally 
known  and  feared  than  the  skunk  (Mephi'tis),  of  which  there 
are  many  species  in  the  United  States.  Their  powerful  means 
of  defense  is  a  pair  of  glands  secreting  a  strong-smelling  fluid, 
which  they  are  able  to  eject  for  a  distance  of  several  feet. 
Though  they  are  destroyed  by  the  farmer  for  robbing  his 
hen-roosts,  they  are  on  the  whole  beneficial,  as  they  feed 
largely  on  injurious  insects.  Those  who  have  observed  them 
most  say  that  they  make  interesting  and  cleanly  pets,  even 
without  the  removal  of  the  scent-glands,  and  that  they  are 
not  prone  to  defend  themselves  except  under  great  provoca- 
tion. The  presence  of  this  means  of  defense  has  had  its  effect 
upon  the  skunk's  character,  insomuch  that  if  a  person  comes 
upon  it  in  the  daytime  it  is  likely  to  make  no  special  effort 
to  escape,  but  goes  about  its  business  leisurely,  secure  in  the 
confidence  that  it  will  not  be  molested.  The  eastern  species 
are  black  animals  about  the  size  of  a  cat,  with  prominent  white 
stripes  down  the  back  and  a  white  patch  on  the  forehead.  The 
white  markings  on  the  black  ground  are  usually  cited  as  an 
example  of  warning  coloration.  It  has  been  asserted  that  it  is 
advantageous  to  the  skunk  to  be  thus  marked,  for  if  it  had 
a  uniform  black  color,  it  might  be  mistaken  in  the  uncertain 
light  for  other  night-prowlers  and  be  pounced  upon  and  killed 
by  an  enemy  before  it  had  an  opportunity  to  use  its  peculiar 
method  of  defense. 

Among  the  aquatic  carnivorous  forms  the  Alaskan  fur-seal 
(Callota'ria  alasca'nus)  has  been  the  subject  of  international 
discussion  on  account  of  the  value  of  its  fur  as  an  article  of 
commerce.  This  is  a  truly  migratory  species  of  mammal, 
bringing  up  its  young  on  the  Pribilof  or  Fur-Seal  Islands  in 


422  GENERAL  ZOOLOGY 

the  summer,  and  going  far  to  sea  in  the  winter.  The  males 
do  not  reach  their  full  size  and  strength  till  about  the  seventh 
year,  and  until  that  age  the  young  males  herd  by  themselves, 
being  forbidden  the  general  herd  by  the  older  males.  The 
females  mature  in  two  years.  Early  in  May  the  full-grown 
males  appear  at  the  islands,  and  the  females  a  few  weeks  after- 
ward. Each  male  immediately  collects  as  many  females  as 
he  can  guard,  and  battles  are  frequent  before  the  groups  are 
made  up.  The  old  males  begin  to  leave  the  beaches  about 
the  middle  of  July.  Seal-hunters  are  restricted  in  their  oper- 
ations to  killing  the  young  males  of  three  years  of  age 
and  upwards.  This  restriction  tends  to  prevent  the  extermi- 
nation of  the  species.  The  fur  is  most  valuable  between  the 
ages  of  three  and  seven  years. 

Insect-Eating  Mammals.  The  insect-eating  mammals,  Insec- 
tiv'ora,  are  usually  of  small  size.  The  teeth  are  sharp  and 
numerous,  and  the  molars  have  sharp  points  for  crushing  the 
bodies  of  insects.  The  eyes  are  often  small  and  hidden  in 
the  fur,  especially  in  the  forms  which,  like  the  moles  and 
shrews,  burrow  in  the  ground.  The  star-nosed  mole  (Con- 
dylu'ra  crista'ta)  is  a  common  American  species  living  in 
peat-swamps  and  rich  land  near  ponds  and  streams.  They 
make  great  burrows,  and  the  earth  thrown  up  may  sometimes 
make  a  pile  a  foot  or  more  in  diameter.  The  name  is  given 
from  a  fleshy  filamentous  appendage  on  the  nostrils,  which 
is  probably  used  as  an  organ  of  touch.  Some  of  the  shrews 
are  the  smallest  mammals  known.  They  generally  live  in 
burrows  like  the  moles.  They  somewhat  resemble  mice,  from 
which  they  can  be  distinguished  by  the  different  plan  of 
the  teeth. 

Bats.  The  Chirop'tera  (Gr.  cheir,  hand ;  pteron,  wing)  are 
marked  off  from  all  other  mammals  by  the  possession  of 
wings,  which  are  formed  of  skin  stretched  over  the  bones  of 
the  arm,  and  including  also  the  legs  and  sometimes  the  tail. 


THE  ALLIES  OF  THE  SQUIRREL:  MAMMALIA     423 


So  well  adapted  for  aerial  locomotion  have  the  bats  (Fig. 
224)  become  that  progress  on  the  ground  is  almost  impossible. 
.The  sense  of  touch  is  greatly  developed  not  only  on  the 
muzzle  but  on  the  wings 
as  well,  so  that  the  animals 
are  able  to  avoid  obstacles 
in  their  nocturnal  flights. 
During  the  day  bats  hang 
themselves  up  by  their  legs 
to  sleep  in  caves  and  in 
hollow  trees.  Some  species 
feed  on  insects,  others  on 
fruit,  and  some,  the  vampire 
bats  of  Central  and  South 
America,  feed  on  blood. 
The  latter  have  the  teeth 
peculiarly  adapted  to  cut- 
ting, the  skin  of  animals. 
The  (Bsophagus  is  so  nar- 
row that  no  solid  matter 
can  pass  down  it. 

Primates.    The  Prima'tes 
(Lat.  primus,  first)  include 
the   monkeys,  apes,  and 
,man.    The  teeth  are  gener- 
ally adapted    to    a  diet  of 


FIG.  224.  Photograph  of  Bat 


both  plant  and  animal  food ;  the  five  toes  and  fingers  are  sepa- 
rate and  are  usually  provided  with  nails;  the  thumb  is  oppos- 
able  to  the  other  digits,  and  the  eyes  are  directed  forward. 

The  spider-monkeys  (At'eles,  Fig.  225)  of  South  and  Cen- 
tral America  are  representative  forms  of  the  New  World 
monkeys.  They  have  a  long  tail,  which  serves  as  an  organ 
of  prehension.  The  most  man-like  of  the  monkeys  are  the 
orang-utan  (Sim'ia  sat'yrus)  of  Borneo  and  Sumatra,  and  the 


424 


GENERAL  ZOOLOGY 


gorilla  (Croril'la  goril'la)  and  chimpanzee  (Anthropopithe'cus 
troglod'ytes)  of  equatorial  Africa.  Of  these  the  chimpanzee 
is  the  most  gentle  in  disposition  and  the  most  intelligent. 
All  these  monkeys  lead  a  more  or  less  arboreal  life  and  build 
nests  in  trees,  where  the  young  are  produced. 


FIG.  225.  Photograph  of  Spider-Monkey 
(American  Museum  of  Natural  History) 

That  man  belongs  zoologically  in  the  same  group  with  the 
monkeys  is  now  universally  admitted,  for  in  the  structural 
characters  upon  which  classification  largely  depends,  as  Prc 
fessor  Huxley  pointed  out  many  years  ago,  he  differs  less 
from  the  apes,  which  resemble  him  most,  than  they  do  from 
other  monkeys.  The  principal  anatomical  characters  are  the 


THE  ALLIES  OF  THE  SQUIRREL:  MAMMALIA     425 

possession  'of  a  relatively  larger  brain-case  and  less-developed 
canine  teeth,  the  adaptation  of  the  vertebral  column  to  an  erect 
posture,  the  greater  length  of  the  lower  as  compared  with  the 
upper  extremities,  and  absence  of  the  power  to  oppose  the 
great  toe  to  the  other  toes.  Some  of  these  differences  seemed 
to  have  been  bridged  over  by  the  discovery  in  1891-1892  of 
the  fossil  remains  of  an  ape-like -man,  or  man-like  ape  (Pithe- 
canthro'pus  erec'tus),  from  the  island  of  Java.  These  remains 
point  to  the  existence  of  an  animal  about  five  and  a  half  feet 
high,  with  a  skull  whose  profile  is  "  roughly  midway  between 
the  skull  of  a  young  chimpanzee  and  the  lowest  human  skull," 
and  whose  brain-capacity  was  nearly  equal  to  that  of  some 
savage  races  of  to-day.  It  is  now  generally  admitted  that  there 
is  but  one  species  of  man  in  the  world  (Ho1  mo  sa'piens),  and 
the  tendency  is  to  group  all  the  different  varieties  into  three 
races,  —  the  Caucasian  of  Europe,  the  Mongolian  of  Asia, 
and  the  Ethiopian  of  Africa. 

Instinct  and  Intelligence  in  Mammals.  There  are  some  who 
ascribe  to  the  birds  and  to  the  mammals  below  man  mental 
attributes,  including  a  power  of  reasoning,  differing  from  the 
attributes  of  man  not  so  much  in  kind  as  in  degree.  Some 
writers  separate  man  quite  distinctly  in  this  regard  from 
the  lower  animals.  Careful  observation  and  experiment  with 
animals  under  conditions  as  nearly  natural  as  possible  is 
needed  before  a  final  answer  can  be  given  to  questions  which 
are  beset  with  the  same  difficulties  that  we  have  noted  in  con- 
nection with  the  study  of  instinct  and  intelligence  in  insects. 

In  order  to  test  whether  dogs  and  cats  exhibit  any  power 
of  reasoning,  Professor  Thorndike,  of  Columbia  University, 
experimented  upon  these  animals  by  inclosing  them  when 
hungry  in  boxes  which  could  be  opened  by  operating  some 
simple  mechanism,  such  as  pulling  a  wire  loop  or  turning  a 
wooden  button.  Freedom  and  food  outside  were  the  motives 
to  escape.  The  experiments  showed  that  in  all  cases  the 


426  GENERAL  ZOOLOGY 

animal  instinctively  clawed  at  the  side  of  the  box,  in  the 
course  of  which  series  of  movements  the  door  would  usually 
be  opened  sooner  or  later.  If  the  animal  was  replaced  in  the 
box  again  and  again,  the  number  of  useless  clawing  actions 
gradually  decreased,  till  finally  the  mechanism  was  operated 
as  soon  as  the  animal  was  put  in  the  box.  If  the  animal  could 
reason,  it  would  be  expected  that  the  box  would  be  opened  at 
once  after  its  first  successful  attempt;  so  Professor  Thorndike 
says :  "  This  sort  of  history  is  not  the  history  of  a  reasoning 
animal.  It  is  the  history  of  an  animal  who  meets  a  certain 
situation  with  a  series  of  instinctive  acts ;  included  without 
design  among  these  acts  is  one  which  brings  freedom  and  food." 

With  this  general  conclusion  Professor  C.  Lloyd  Morgan, 
in  his  Animal  Behavior,  agrees.  This  author  says:  "As  at 
present  advised,  therefore,  I  see  no  reason  for  withdrawing 
from  the  position  provisionally  taken  up.  The  utilization  of 
chance  experience,  without  the  framing  and  application  of 
an  organized  scheme  of  knowledge,  appears  to  be  the  pre- 
dominant method  of  animal  intelligence." 

In  their  mental  attributes  monkeys  seem  to  occupy  an 
intermediate  position  between  man  and  the  lower  mammals. 
Some  of  the  observations  made  on  this  subject  have  been 
thus  summed  by  Professor  R.  Ramsay  Wright,  of  Toronto 
University.  "  Sympathy  has  been  observed  in  many  forms. 
The  female  gorilla  has  been  said  to  die  of  grief  when  the 
young  is  taken  away  ;  orangs  have  come  in  a  body  to  beg  for 
the  corpse  of  a  dead  companion,  gibbons  for  a  wounded  com- 
rade. A  female  gibbon  has  been  observed  to  wash  the  face 
of  her  young,  a  Cebus  to  brush  off  flies  from  the  face  of  hers 
while  sleeping,  and  all  monkeys  assist  each  other  with  the 
utmost  zeal  in  the  search  for  intruders  in  their  hair.  They 
have  been  noticed  to  feed  each  other,  to  carry  food  to  sick 
monkeys,  and  to  adopt  orphans.  More  remarkable  than  all, 
a  monkey  has  been  seen  to  throw  a  rope  to  a  comrade  who 


THE  ALLIES  OF  THE  SQUIRREL:  MAMMALIA    427 

had  fallen  overboard.  That  all  monkeys  are  fond  of  play, 
especially  when  young,  is  notorious  ;  they  have  a  keen  sense 
of  the  ludicrous  and  enjoy  exciting  laughter,  but  they  resent 
being  jeered  at  and  may  revenge  themselves,  as  in  the  case 
of  a  Cape  baboon,  who  bespattered  with  mud  an  officer  in 
his  dress  uniform  who  had  offended  him." 

Professor  Thorndike  closes  an  article  in  the  Popular  Science 
Monthly  for  July,  1901,  in  a  way  which  serves  to  bring  out 
the  intermediate  position  of  the  monkeys  between  man  and 
the  lower  mammals.  He  says  :  "  In  their  method  of  learning, 
although  monkeys  do  not  reach  the  human  stage  of  a  rich 
life  of  ideas,  yet  they  carry  the  animal  method  of  learning, 
by  the  selection  of  impulses  and  association  of  them  with 
different  sense-impressions,  to  a  point  beyond  that  reached 
by  any  other  of  the  lower  animals.  In  this,  too,  they  resem- 
ble man  ;  for  he  differs  from  the  lower  animals  not  only  in 
the  possession  of  a  new  sort  of  intelligence  but  also  in  the 
tremendous  extension  of  that  sort  which  he  has  in  common 
with  them.  A  fish  learns  slowly  a  few  simple  habits.  Man 
learns  quickly  an  infinitude  of  habits  that  may  be  highly 
complex.  Dogs  and  cats  learn  more  than  the  fish,  while 
monkeys  learn  more  than  they.  In  the  number  of  things  he 
learns,  the  complex  habits  he  can  form,  the  variety  of  lines 
along  which  he  can  learn  them,  and  in  their  permanence 
when  once  formed,  the  monkey  justifies  his  inclusion  with 
man  in  a  separate  mental  genus." 

Economic  Importance  of  Mammals.  The  mammals  come 
into  more  intimate  relations  with  man  than  any  other  group 
of  animals.  From  them  he  gets  materials  for  dress,  —  wool, 
leather,  and  furs ;  food  in  the  shape  of  butter,  cheese,  and 
meat  of  different  kinds.  They  are  his  beasts  of  burden  the 
world  over,  and  they  furnish  a  long  line  of  miscellaneous 
products  such  as  horn,  bone,  ivory,  perfumes,  whalebone, 
oils,  fats,  and  material  for  fertilizers. 


428  GENERAL  ZOOLOGY 

Geological  Development  of  Mammals.  With  the  upheaval 
of  the  Rocky  Mountain  system  at  the  close  of  Mesozoic 
time  the  North  American  continent  assumed  practically  its 
present  outline,  with  the  exception  of  a  strip  along  the  south- 
eastern coast,  which  was  still  beneath  the  level  of  the  ocean 
(see  map,  p.  363).  In  connection  with  this  disturbance  of 
level  and  the  accompanying  climatic  changes  the  great  rep- 
tiles so  characteristic  of  the  period  became  extinct  and  left 
the  field  clear  for  the  development  of  the  mammals.  The 
succeeding  period  is  therefore  called  the  Age  of  Mammals. 
As  we  have  already  seen,  representatives  of  each  group  of 
animals  have  appeared  before  the  age  which  bears  its  name, 
so  the  first  mammals  of  which  we  have  any  knowledge  are 
to  be  credited  to  the  Age  of  Reptiles.  They  were  nearly  all 
of  small  size  and  allied  to  the  marsupials  and  monotremes 
of  to-day,  —  groups  which  we  have  noticed  as  being  the 
lowest  of  the  class. 

During  the  Age  of  Mammals  there  were  extensive  areas 
of  fresh- water  lakes  in  western  North  America,  shown  by  the 
shaded  areas  on  the  map  on  page  363.  It  is  from  these  deposits 
that  much  of  our  information  regarding  the  early  mammals 
of  America  has  been  obtained.  The  American  Museum  of 
Natural  History  in  New  York  City  has  on  exhibition  a  large 
series  of  fossils  from  this  region.  Many  of  the  specimens 
discovered  are  of  generalized  structure;  that  is,  they  possess 
the  characteristics  of  several  different  groups  of  to-day,  with- 
out much  special  adaptation  or  modification  to  a  particular 
kind  of  life  or  food.  It  is  among  such  animals  that  we  must 
look  for  the  ancestors  of  the  species  of  to-day,  for  no  species 
of  mammal  which  was  in  existence  in  the  Age  of  Mammals 
has  lasted  through  to  the  present  time. 

Of  no  other  animal  have  we  so  complete  and  satisfactory 
a  geological  record  as  in  the  case  of  the  horse.  From  fossil 
remains  found  in  the  western  part  of  the  United  States  we 


THE  ALLIES  OF  THE  SQUIRREL:  MAMMALIA     429 


are  able  to  trace  its  evolution  from  an  ancestor  (ProtoroTiip1- 
pus,  Fig.  226)  a  little  larger  than  a  cat,  with  four  toes  on 
the  front  feet  and  three  on  the  hind  feet.  The  figure  of 
Protorohippus  is  photographed  from  a  water-color  by  Mr. 
Charles  II.  Knight,  based  on  skeletal  material  at  the  Amer- 
ican Museum  of  Natural  History.  The  markings  are  drawn 
as  they  are  supposed  to  have  existed  on  the  animal.  There  is 


FIG.  226.  Protorohippus 
(American  Museum  of  Natural  History) 

reason  to  believe  that  the  undiscovered  ancestors  of  this  early 
form  had  five  toes  on  each  foot.  The  transition  to  the  horse 
of  to-day  has  been  accomplished  by  a  gradual  increase  of  size, 
a  reduction  in  the  number  of  toes,  and  a  reduction  in  number 
and  an  increase  of  complexity  in  the  teeth.  The  main  steps 
in  the  evolution  of  the  bones  of  the  feet  are  shown  in  Fig.  227. 
The  changes  in  the  limbs  are  in  the  nature  of  adaptations 
fitting  the  animal  for  rapid  locomotion  over  level,  grassy 


430 


THE  ALLIES  OF  THE  SQUIRREL:  MAMMALIA     431 

areas.  The  increased  complexity  of  the  teeth  makes  them 
more  efficient  grinding-organs.  In  the  latter  part  of  the  Age 
of  Mammals  North  America  was  broadly  connected  with  Asia, 
and  the  horse  is  known  to  have  inhabited  plains  of  all  the 
continents  excepting  Australia.  After  the  horse  had  reached 
practically  its  present  state  of  development  (in  the  early  part 
of  the  next  succeeding  period,  the  Age  of  Man)  it  seems  to 
have  disappeared  entirely  from  America,  owing  to  causes  not 
thoroughly  understood,  though  generally  ascribed  to  the 
oncoming  cold  of  the  Glacial  Epoch.  The  horse  persisted, 
however,  in  Europe,  and  was  one  of  the  animals  which  prim- 
itive man  domesticated.  The  various  uses  to  which  the  horse 
could  be  put  were  gradually  learned  by  man,  for  Professor 
Osborn,  of  the  American  Museum  of  Natural  History,  says 
there  is  "  abundant  proof  that  man  first  hunted  and  ate,  then 
drove,  and  finally  rode  the  animal."  It  was  reintroduced  into 
America  by  the  Spaniards  at  the  time  of  their  conquest,  and 
soon  ran  wild. 

The  carnivores  were  early  represented  by  generalized 
types,  and  later  by  dogs  and  saber-toothed  cats.  The  latter 
get  their  name  from  their  lengthened  canine  teeth.  Insec- 
tivorous mammals,  rodents,  bats,  ungulates  of  many  kinds, 
and  even  the  primates  also  occurred,  and  in  the  waters  of  the 
oceans  were  found  cetaceans  of  different  species. 

The  Age  of  Mammals  began  in  North  America  with  a 
warm  climate,  as  in  the  case  of  previous  periods,  but  toward 
its  close  frigid  conditions  began  to  prevail,  probably  due  to 
the  gradual  elevation  of  the  continental  land-mass.  The  on- 
coming cold  produced  in  the  northern  part  of  both  America 
and  the  Eurasian  land-mass  conditions  so  severe  that  to  the 
period  the  name  Glacial  Epoch  is  given.  During  its  contin- 
uance all  of  North  America  north  of  a  line  drawn  from 
New  York  through  Pennsylvania,  Indiana,  Missouri,  South 
Dakota,  Montana,  and  Oregon,  was  covered  at  different  times 


432 


THE  ALLIES  OF  THE  SQUIRREL:  MAMMALIA     433 

with  a  layer  of  ice,  which  in  certain  regions  grew  to  be  a 
mile  thick  over  the  land,  destroying  all  life  or  forcing  it  to 
migrate  southward  to  escape  the  rigors  of  the  climate.  As 
there  were  several  invasions  and  retreats  of  the  ice,  there 
may  be  said  to  have  been  several  glacial  epochs,  separated 
by  long  periods  of  warmer  weather,  when  the  animal  and 
plant  life  could  slowly  work  its  way  back  on  the  edge  of 
the  retreating  glaciers.  There  is  a  peculiar  interest  to  this 
period,  inasmuch  as  it  introduces  the  last  of  the  great  geo- 
logical eras,  the  Quaternary  Period,  or  the  Age  of  Man. 

A  conspicuous  feature  of  the  mammalian  life  of  the  Age 
of  Man  was  the  great  size  of  many  of  the  species.  After  the 
opening  glacial  epoch  the  climate  became  mild  again,  and 
this  seems  to  have  favored  the  development  of  abundant 
vegetation  and  great  mammalian  forms.  One  of  the  largest 
and  most  widely  distributed  species  was  the  Mammoth 
(EVephas  primige'nius,  Fig.  228),  a  proboscidean  larger  than 
the  elephant  of  to-day  and  covered  with  a  thick  coat  of 
hair,  an  adaptation  to  cold  temperate  regions.  Its  remains 
have  been  found  frozen  in  the  ice  of  Siberia,  the  hair  and 
flesh  perfectly  preserved.  Early  man  knew  of  this  great 
mammal,  for  a  drawing  of  the  creature  is  in  existence, 
made  on  a  piece  of  its  own  tusk  (Fig.  229).  The  mastodons 
were  somewhat  similar  to  the  mammoths,  but  fitted  on  the 
whole  for  a  warmer  climate.  There  are  over  thirty  species 
of  mastodons  known,  of  nearly  world-wide  distribution. 
They  have  become  extinct  within  so  short  a  time,  geologi- 
cally speaking,  that  traditions  of  their  existence  as  living 
animals  occur  among  men. 

The  remains  of  giant  edentates  have  been  found  in  South 
America.  Recent  discoveries  seem  to  show  that  some  of  them 
were  living  within  the  period  of  man  on  that  continent,  for 
some  of  the  tribes  of  South  American  Indians  have  traditions 
respecting  these  monsters.  In  Europe  and  Asia  there  were 


434 


GENERAL  ZOOLOGY 


lions,  hyenas,  bears,  rhinoceroses,  and  gigantic  ungulates.  In 
Australia,  as  will  be  expected  from  what  has  been  said  of  the 
distribution  of  the  group,  there  were  marsupials  of  various 
species. 

But  the  great  interest  of  the  Quaternary  Period  centers 
about  man.  If  it  is  not  yet  possible  to  prove  to  the  satisfac- 
tion of  every  one  the  existence  of  man  in  the  Glacial  Epoch 
in  North  America,  it  is  certain  that  he  was  in  existence  in 
Europe  at  that  time.  It  would  be  interesting  to  know,  if 
possible,  how  far  distant  we  should  place  this  period,  and 


FIG.  229.  Primeval  Drawing  of  Mammoth  on  Mammoth  Tusk 
(From  Lucas'  Animals  of  the  Past) 

where  man  first  appeared  on  the  earth,  but  to  neither  of  these 
questions  can  any  satisfactory  answer  be  given.  Regarding 
the  time,  estimates  have  been  made  in  various  ways,  reaching 
conclusions  which  vary  greatly.  A  conservative  estimate  is 
that  the  Glacial  Epoch  began  two  million  four  hundred  thou- 
sand years  ago  and  ended  eighty  thousand  years  ago.  Regard- 
ing the  place  of  man's  origin,  it  has  been  asserted  that  his 
earliest  home  was  Africa,  because  the  great  apes,  which  most 
resemble  him,  live  there  to-day ;  or  that  it  was  somewhere  in 
equatorial  regions,  where  the  vegetation  is  abundant  and  the 
climate  quite  similar  throughout  the  year ;  others  claim  that 
it  was  on  some  of  the  high  plains  of  the  temperate  zone,  like 


THE  ALLIES  OF  THE  SQUIRREL:  MAMMALIA     435 

those  of  Persia  and  Tibet.  After  all,  the  study  of  the  condi- 
tions under  which  he  lived  is  a  more  important  subject  than 
the  discussion  of  either  the  time  or  place  of  his  origin. 

Primitive  man  was  a  savage,  living  in  caves.  His  princi- 
pal means  of  defense,  in  addition  to  those  with  which  nature 
had  provided  him,  were  a  stone  picked  from  the  ground  or  a 
bough  broken  from  a  tree.  At  an  early  stage  in  his  develop- 
ment he  learned  the  use  of  fire,  made  clothing  of  the  skins  of 
wild  beasts  to  keep  himself  warm,  and  fashioned  rude  imple- 
ments out  of  bone,  shell,  horn,  wood,  and  stone.  In  those 
places  where  such  easily  worked  metals  as  copper  and  zinc 
were  accessible  man  early  learned  their  use  and  made  from 
them  implements  of  bronze,  a  compound  of  the  two  metals. 
From  a  hunting  existence  arose  the  nomadic  or  wandering 
life,  with  property  in  the  shape  of  herds  of  domesticated  or 
semidomesticated  animals,  and  the  more  fixed  agricultural 
condition  in  which  the  main  dependence  for  food  was  on  the 
products  of  the  field.  We  see  people  to-day  in  each  of  these 
conditions  of  existence.  Along  with  the  advance  in  the  mode 
of  life  has  gone  a  mental  and  moral  evolution  as  man's  con- 
quest of  nature  has  been  pushed  through  wider  and  wider 
fields. 


CHAPTER  XXXII 
THE  HISTORICAL  DEVELOPMENT  OF  ZOOLOGY 

The  present  generation  finds  itself  the  heir  of  a  vast  patrimony  of  science ; 
and  it  must  needs  concern  us  to  know  the  steps  by  which  these  possessions 
were  acquired,  and  the  documents  by  which  they  are  secured  to  us  and  our 
heirs  forever.  —  WHEWELL,  History  of  the  Inductive  Sciences. 

Divisions  of  the  Science  of  Zoology.  Zoology  is  the  science 
that  treats  of  animals.  It  is  a  sister  science  of  botany,  which 
deals  with  the  plant  world.  Both  botany  and  zoology  are 
branches  of  biology,  the  science  which  has  to  do  with  living 
things.  The  various  ways  in  which  animals  may  be  consid- 
ered by  man  give  rise  to  the  different  divisions  of  the  science 
of  zoology.  Thus  the  study  of  the  structure  of  the  organs  of 
animals  is  comparative  anatomy,  or  morphology ;  the  study 
of  the  functions  of  the  organs  (such  as  nutrition,  growth,  and 
reproduction)  is  comparative  physiology.  The  consideration 
of  the  mental  phenomena  of  animals  is  the  field  of  compara- 
tive psychology.  The  geographical  distribution  of  animals  deals 
with  the  fauna  of  the  different  land-areas  ;  the  geological  dis- 
tribution (paleontology),  with  the  animal  life  of  past  eras.  The 
study  of  the  relations  of  animals  to  each  other,  to  plants, 
and  to  their  inorganic  environment,  is  ecology.  Under  the 
name  of  bionomics,  Professor  E.  Ray  Lankester  has  defined 
this  as  "  the  lore  of  the  farmer,  gardener,  sportsman,  and 
field  naturalist."  To  show  the  blood-relationships  of  the  dif- 
ferent members  of  the  kingdom,  animals  are  arranged  in 
groups,  or  classified ;  this  division  of  the  subject  is  system- 
atic zoology.  The  consideration  of  the  uses  of  animals  to  man 
is  the  field  of  economic  zoology.  Finally,  the  inquiry  after 
the  causes  of  the  various  phenomena  of  nature  is  etiology. 

436 


HISTORICAL  DEVELOPMENT  OF  ZOOLOGY     437 

Zoologists  are,  of  course,  interested  to  understand,  as  far  as 
they  can,  the  phenomena  exhibited  by  the  animal  kingdom. 
We  have  called  attention  to  some  of  these  efforts  at  explana- 
tion in  Chapter  X. 

It  will  serve  to  give  us  the  historical  perspective  which 
will  enable  us  to  better  appreciate  the  great  mass  of  informa- 
tion available  for  us  to-day,  if  we  pass  in  brief  review  the 
main  steps  in  the  development  of  this  body  of  knowledge. 
We  shall  gain  thereby  some  insight  into  the  method  of  scien- 
tific research,  and  shall  be  helped  to  see  the  limitations  of 
our  knowledge  and  to  appreciate  the  problems  which  are 
now  pressing  for  solution. 

Zoology  among  the  Greeks  and  Romans.  In  our  survey  we 
need  not  go  farther  back  than  the  time  of  the  Greeks,  for  it 
was  there,  though  in  no  systematic  form,  that  the  beginnings 
of  modern  zoology  were  laid.  The  Greeks'  knowledge  of 
animals  grew  from  humble  beginnings  in  an  early  prehistoric 
period,  and  reached  its  culmination  in  the  philosopher  Aris- 
totle (384-322  B.C.,  Fig.  230).  Though  the  Greeks  early 
showed  a  lively  scientific  curiosity  and  a  desire  to  explain 
the  world  of  matter  and  life  by  ascribing  phenomena  to  natu- 
ral causes,  they  generally  failed  to  appreciate  the  necessity 
for  careful  observation  of  a  long  series  of  individual  facts 
before  proceeding  to  explain  those  facts  by  reference  to  a 
general  law. 

Aristotle's  name  is  the  greatest  among  Greek  scientists 
partly  because  he  appreciated  this  need.  He  laid  great  stress 
upon  the  importance  of  what  is  called  the  inductive  method 
in  the  pursuit  of  scientific  knowledge.  This  method  demands, 
first,  careful  observation  of  a  wide  range  of  facts  ;  second,  the 
study  of  those  facts  with  reference  to  each  other,  to  bring 
out  the  essential  and  to  eliminate  the  nonessential  elements ; 
and  finally,  the  explanation  of  the  facts  observed,  by  a. state- 
ment of  the  law  involved.  Aristotle  protested  against  the 


438 


GENERAL  ZOOLOGY 


separation  of  theory  and  fact,  which  invariably  occurs  when 
theories  are  not  put  to  the  test  of  agreement  with  the 
facts.  "We  must  not,"  he  said,  "accept  a  general  prin- 
ciple from  logic  only,  but  must  prove  its  application  to 
each  fact;  for  it  is  in  facts  that  we  must  seek  general  prin- 
ciples, and  these  must  always  accord  with  facts."  Though 

so  clearly  stated,  the 
principle  was  forgot- 
ten by  the  world  until 
it  was  restated  by 
Francis  Bacon  (1561- 

M  '^^^i  Ilk      I626)   in  the   seven- 

J||  II     teenth  century.    To  be 

•  B    sure,  the  English  Fran- 

•  ciscan  monk,   Roger 

•  Bacon   (1214-1292), 
appreciated  the   neces- 

BP|M  mj    sity   of   observation   in 

^r^'^-mfm      nature,   and   himself 
JjHl  if       applied  the  inductive 

^B;  jf  I         al^r         method  in  some  of  his 

m  dr      /  Ji  work,  but  the  time  was 

not  then  ripe  for  a 
general  appreciation  of 
the  importance  of  the 
principle. 

Aristotle  also  owes  his  preeminence  over  other  Greek 
writers  on  natural  history  to  the  variety  and  extent  of  his 
own  observations,  to  his  voluminous  collection  of  the  obser- 
vations and  statements  of  others,  and  to  his  theories  of  life, 
which  are  curiously  anticipatory  of  some  features  of  modern 
evolutionary  views.  To  refer  first  to  his  own  observations, 
it  has  been  computed  from  Aristotle's  works  that  he  was 
more  or  less  acquainted  with  over  five  hundred  species  of 


FIG.  230.  Aristotle 


HISTORICAL  DEVELOPMENT  OF  ZOOLOGY     439 

animals,  though  he  was  unable  to  classify  them  except  in  a 
superficial  way.  His  lack  of  an  exact  knowledge  of  anatomy 
rendered  anything  like  a  natural  classification  impossible. 
He  was,  however,  familiar  with  the  external  appearance  of 
many  organs  and  was  able  to  note  the  adaptation  of  organs 
to  different  functions.  His  writings  consist  not  only  of  his 
own  observations  but  also  of  statements  about  animals  taken 
from  every  source,  and  many  of  these,  it  must  be  confessed, 
seem  to  us  of  to-day  so  plainly  untrue  and  impossible  of 
belief  that  it  is  difficult  for  us  to  understand  how  they 
could  have  been  credited  by  the  philosopher  whose  vision 
extended  so  widely.  However,  Aristotle's  History  of  Ani- 
mals was  the  source,  as  we^shall  see,  from  which,  for  many 
centuries,  much  of  the  natural-history  lore  of  Europe  was 
drawn.  The  question  concerning  a  disputed  point,  then, 
was  not,  What  do  the  facts  say?  but,  What  is  written  in 
Aristotle  ? 

It  has  just  been  said  that  Aristotle  held  views  suggestive 
of  those  of  modern  evolutionists.  Though  he  could  not  .have 
had  a  sufficient  basis  of  facts  from  which  to  draw  conclu- 
sions, he  yet  conceived  of  a  complete  gradation  in  nature, 
beginning  with  the  inorganic  world,  passing  through  the 
plants  to  animals,  and  ending  with  man.  Like  others  of  his 
time,  Aristotle  believed  in  the  development  of  living  from 
non-living  matter  (spontaneous  generation),  and  he  pictured 
the  change  as  taking  place  directly,  even  with  some  of  the 
higher  animals.  With  much  that  is  false  and  mistaken,  enough 
of  value  and  brilliancy  remains  in -the  work  of  Aristotle  to 
entitle  him  to  be  called  the  founder  of  zoology. 

Passing  mention  should  be  made  of  one  other  Greek, 
the  philosopher  and  physician  Galen  (born  A.D.  130).  He 
deserves  credit  for  being  the  first  to  insist  that  medicine 
must  rest  on  a  knowledge  of  anatomy  and  physiology.  Dis- 
section of  the  human  body  being  forbidden,  he  examined  the 


440  GENERAL  ZOOLOGY 

bodies  of  monkeys  and  swine  as  being  near  to  man  in  struc- 
ture. His  work  represents  the  highest  attainments  of  Greek 
medicine. 

The  genius  of  Rome  was  not  manifested  along  the  line  of 
biology,  and  there  is  in  the  whole  course  of  Roman  history 
no  really  great  name  in  this  science.  We  may  mention,  how- 
ever, the  Roman  naturalist  Pliny  (born  A.D.  23),  who  lost 
his  life  while  attempting  to  approach  Vesuvius  during  the 
great  eruption  in  A.D.  79,  which  overwhelmed  the  cities  of 
Herculaneum  and  Pompeii.  Pliny  was  not  so  much  an  origi- 
nal observer  as  a  voluminous  writer  and  collector  of  the  opin- 
ions of  others.  His  books  are  a  great  storehouse  of  the  facts 
and  fancies  of  antiquity. 

The  Middle  Ages.  History  tells  how  Greece  was  conquered 
by  Rome,  to  what  height  Rome  attained,  and  how  the  down- 
fall of  the  Western  Roman  Empire  in  A.D.  476  brought  to  a 
close  the  ancient  history  of  Europe  and  ushered  in  a  new 
civilization  built  on  the  ruins  of  the  old.  The  period  from 
the  fifth  to  the  sixteenth  century  is  usually  spoken  of  as  the 
Middle  Ages.  In  the  early  part  of  this  period  (from  the  fifth 
to  the  eleventh  century,  often  called  the  Dark  Ages)  the 
many  wars  left  little  time  for  the  pursuit  of  science.  The 
habit  of  observing  natural  phenomena  and  the  desire  to  seek 
an  explanation  had  given  place  to  a  slavish  acceptance  of  the 
statements  of  others.  Blind  adherence  to  authority  reigned 
everywhere.  In  all  this  time  no  new  fact  of  importance  ap- 
pears in  the  history  of  our  science ;  no  great  original  student 
of  the  subject  was  born. 

While  Europe  was  in  this  condition  of  darkness  the  Ara- 
bians, originally  a  shepherd  race,  stirred  to  national  life  by 
their  prophet,  Mohammed  (born  A.D.  570  or  571),  began  a 
long  series  of  wars,  which  resulted  in  the  conquest  of  a  large 
part  of  western  Asia  and  northern  Africa.  They  even  pushed 
their  way  into  Europe,  conquering  the  whole  of  the  peninsula 


HISTORICAL  DEVELOPMENT  OF  ZOOLOGY     441 

of  Spain,  with  the  exception  of  a  few  mountainous  districts 
in  the  north.  During  the  period  of  their  greatest  power  the 
Arabians  alone,  of  all  the  races  of  Europe,  kept  alive  the 
spirit  of  science.  They  preserved  many  classical  works  from 
destruction,  especially  those  of  medicine,  by  translating  them 
into  Arabic.  The  power  of  the  Arabians  came  to  an  end  in 
Europe  in  1491,  when  Granada,  their  last  stronghold,  was 
torn  from  their  grasp  by  Ferdinand  and  Isabella. 

During  the  closing  centuries  of  the  Middle  Ages  many 
events  prepared  the  way  for  the  new  interest  in  science 
characteristic  of  the  sixteenth  and  seventeenth  centuries. 
The  many  political  adjustments  of  the  period  molded  the 
nations  of  Europe  into  much  the  same  form  as  we  know  them 
to-day.  The  application  of  the  mariner's  compass  to  naviga- 
tion made  voyages  to  new  lands  possible.  America  was  dis- 
covered by  Columbus ;  Magellan's  ship  sailed  round  the 
world.  As  a  result  of  the  general  intellectual  awakening 
the  bonds  of  authority  were  weakened  and  men  began  to 
think  for  themselves.  Printing  was  invented,  and  then  fol- 
lowed a  wide  dispersion  of  the  knowledge  of  the  ancients. 
Universities  were  founded,  to  which  flocked  students  from 
all  over  Europe,  eager  to  drink  in  the  new  learning. 

Zoology  of  the  Sixteenth  Century.  With  the  sixteenth 
century  we  are  fairly  adrift  on  the  stream  of  modern  science. 
One  of  the  earliest  investigators  was  Andreas  Vesalius,  born 
in  1514  at  Brussels.  He  became  interested  in  anatomy  while 
only  a  boy  and  studied  the  human  body  from  dissections, 
though  often  experiencing  considerable  difficulty  in  getting 
material.  In  1540  he  became  professor  of  anatomy  in  the 
University  of  Padua,  in  northern  Italy,  and  two  years  later, 
when  twenty-eight  years  of  age,  he  published  his  Great  Anat- 
omy, illustrated  with  woodcuts  by  the  best  Italian  artists  of 
his  time.  Having  had  the  advantage  of  making  dissections, 
he  was  able  to  point  out  errors  in  the  work  of  Galen,  who 


442  GENERAL  ZOOLOGY 

had  been  forced  to  study  the  lower  forms.  With  Vesalius 
and  his  contemporaries  modern  anatomy  may  be  said  to  have 
begun. 

Konrad  von  Gesner  (1516-1565),  born  at  Zurich,  Switzer- 
land, had  a  wide  interest  in  natural  history.  He  was  a  poor 
boy,  left  an  orphan,  and  his  early  life  was  one  constant  strug- 
gle with  poverty.  Conquering  all  difficulties,  so  great  was 
his  enthusiasm  for  science,  he  rose  to  be  professor  of  natural 
history  in  his  native  city.  He  made  collections  of  animals 
and  plants,  and  published  (1551—1558)  a  great  History  of  Ani- 
mals, in  which  he  described  all  the  animals  then  known,  with 
statements  concerning  their  structure  and  habits,  some  details 
of  their  physiology,  and  their  economic  importance.  This 
was  the  first  comprehensive  work  on  natural  history  since 
the  time  of  Aristotle. 

Zoology  of  the  Seventeenth  Century.  To  William  Harvey 
(1578-1657),  an  Englishman  who  studied  at  Padua  under  a 
pupil  of  Vesalius,  we  are  indebted  for  the  first  accurate  state- 
ment of  the  circulation  of  the  blood  in  man.  Galen  had  shown 
the  existence  of  blood  in  the  arteries,  and  Harvey's  professor 
at  Padua  had  confirmed  the  existence  of  the  valves  in  the 
course  of  the  venous  circulation,  pointed  out  by  a  still  earlier 
investigator ;  but  it  was  left  to  Harvey's  painstaking  observa- 
tions to  follow  the  course  of  the  blood  from  the  heart  to  the 
lungs,  from  the  lungs  back  to  the  heart,  and  thence  all  over 
the  body.  Harvey's  discovery  was  made  in  1614  and  pub- 
lished in  1628,  after  his  return  to  London,  where  he  practiced 
as  a  physician.  Like  many  another  discovery  in  science,  it 
at  first  aroused  hostile  criticism.  From  this  period  the  rise 
of  animal  physiology  may  be  dated.  Harvey  also  studied  the 
development  of  the  chick  in  the  egg,  arid  may  be  said  to  be 
the  founder  of  modern  embryology.  Of  course  he  did  not 
understand  the  egg  as  well  as  we  understand  it  to-day,  since 
he  believed  in  spontaneous  generation. 


HISTORICAL  DEVELOPMENT  OF   ZOOLOGY     443 


In  the  early  part  of  the  seventeenth  century  (1609)  Galileo 
used  the  telescope,  bringing  distant  worlds  within  our  nearer 
view.  AVhat  the  telescope  was  to  astronomy  the  microscope 
was  to  zoology.  The  invention  of  the  microscope,  about  1600, 
is  usually  credited  to  Zacharias  Janssen,  a  Dutch  spectacle- 
maker;  it  was  used  in  the  study  of  animals  by  Malpighi 
(1628-1694),  an  Italian 
anatomist,  about  1661. 
Among  other  subjects 
he  studied  the  capillary 
circulation,  which  Avas 
beyond  the  power  of 
Harvey  with  only  his 
simple  lens.  In  Eng- 
land the  labors  of  John 
Ray  (1628-1705)  added 
greatly  to  our  knowl- 
edge of  animals.  Ray 
was  the  first  to  define 
the  use  of  the  word 
"  species."  He  laid  the 
foundations  of  system- 
atic zoology. 

Zoology  of  the  Eight- 
eenth Century.  To 
Linnaeus  (1707-1778, 
Fig.  231)  is  due  the 
credit  for  the  invention  of  the  binomial  nomenclature.  Before 
this  time  there  had  been  the  greatest  confusion  among  natu- 
ralists as  to  the  names  of  animals  and  plants.  Not  only  were 
the  names  themselves  cumbersome,  but  there  was  no  uni- 
formity in  their  use.  Linnasus  also  saw  the  need  of  groups 
higher  than  species,  and  he  put  classification  on  a  more  exact 
basis  by  recognizing  and  defining  six  classes  of  animals, — 


FIG.  231.  Linnaeus 


444  GENERAL  ZOOLOGY 

mammals,  birds,  amphibians  (including  reptiles),  fishes,  insects 
(including  all  arthropods),  and  Vermes  (including  mollusks, 
worms,  echinoderms,  coelenterates,  and  protozoans).  He  be- 
lieved in  the  fixity  of  species,  teaching  at  first  that  there  are 
as  many  species  of  animals  as  were  created  in  the  beginning. 
Subsequent  editions  of  his  System  of  Nature  (first  published 
as  a  pamphlet  in  1735)  showed  slight  modifications  of  this 
view,  but  on  the  whole  his  influence  was  in  behalf  of  the  idea 
of  the  fixity  of  species. 

Buffoii  (1707-1788)  was  destined  to  exert  as  great  an 
influence  on  zoology  as  did  Linnaeus,  but  in  a  different  field. 
Buffon's  studies  were  widely  extended  over  nature.  His 
Natural  History  is  a  popular  account  of  the  animal  kingdom 
most  interestingly  written.  It  was  read  very  generally  and 
did  much  to  popularize  the  subject.  Buffon  was  one  of  the 
first  to  attempt  an  explanation  of  the  facts  of  the  geograph- 
ical distribution  of  animals,  and  he  is  considered  the  first  of 
the  great  pioneers  of  modern  evolution.  Professor  Osborn, 
in  his  history  of  the  development  of  the  evolution  idea,  From 
the  G-reeks  to  Darwin,  says:  "  It  is  interesting  to  contrast  these 
two  great  men  [Linnaeus  and  Buffon],  one  the  founder  of  the 
view  of  classification-  as  a  fixed  system  of  the  divine  order 
of  things,  and  the  ne  plus  ultra  of  botany  and  zoology;  the 
other  the  founder  of  the  directly  opposed  view  of  classifica- 
tion as  an  invention  of  man,  and  of  the  laws  governing  the 
relation  of  animals  to  their  environment  as  the  chief  end  of 
science."  As  might  be  expected  at  this  period  Buffon  was 
not  an  unqualified  evolutionist  but  wavered  between  views 
such  as  Linnaeus  held  and  a  belief  in  the  mutability  (liability 
to  change)  of  species. 

One  of  the  earliest  writers  in  the  field  which  we  have  termed 
ecology  or  bionomics  was  the  English  clergyman,  Gilbert 
White  (1720-1793),  the  author  of  The  Natural  'History 
and  Antiquities  of  Selborne.  Though,  as  Professor  J.  Arthur 


HISTORICAL  DEVELOPMENT  OF   ZOOLOGY     445 

Thomson  points  out,  White  was  "  the  prototype  of  the  better 
class  of  modern  amateurs,"  still  the  out-of-door  study  of  ani- 
mals "rarely  attained  either  dignity  or  definiteness  until 
Darwin  demonstrated  its  importance." 

Animal  electricity  was  discovered  by  Galvani  (1737-1798), 
professor  of  anatomy  at  Bologna.  His  attention  is  said  to 
have  been  called  to  the  subject  by  his  wife.  She  was  prepar- 
ing frogs'  legs  for  the  table  near  an  electric  machine  in  opera- 
tion, and  noticed  that  when  the  legs  were  touched  by  the 
knife  they  twitched  violently. 

Zoology  of  the  Nineteenth  Century.  The  science  of  zoology 
developed  so  rapidly  from  the  beginning  of  the  eighteenth 
century  that  it  will  be  impossible  now  to  do  more  than  call 
attention  to  a  very  few  of  the  most  important  discoveries  and 
the  men  to  whom  they  are  accredited.  A  dominating  figure 
in  the  early  part  of  the  nineteenth  century  was  Georges  Cuvier 
(1769-1832),  a  French  naturalist  whose  influence  was  exerted 
along  many  different  lines.  By  his  studies  of  fossils,  recog- 
nizing them  as  the  remains  of  animals  of  past  times,  and 
related  to  the  animals  of  to-day,  he  founded  paleontology. 
He  also  stated  the  principle  of  the  correlation  of  parts,— 
a  conception  which  pictures  the  animal  as  a  unit  rather 
than  a  fortuitous  collection  of  separate  parts.  While  he  un- 
doubtedly carried  the  principle  beyond  its  legitimate  limits, 
there  can  be  no  question  as  to  its  important  influence  on 
the  history  of  zoology.  Cuvier  recognized  the  importance 
of  anatomical  structure  as  a  basis  for  classification.  He  also 
knew  a  second  basis  in  paleontology,  a  fact  just  referred  to. 
Cuvier  divided  the  animal  kingdom  into  four  groups, — Ver- 
tebrata,  Mollusca,  Articulata,  and  Radiata. 

During  the  nineteenth  century  important  discoveries  paved 
the  way  for  a  better  understanding  of  the  minute  structure 
of  the  animal  body  and  the  physiology  of  its  units  of  struc- 
ture, the  cells.  In  1838  Schleiden  showed  that  plants  were 


446  GENERAL  ZOOLOGY 

made  up  of  very  small  parts  called  cells,  and  the  next  year 
Schwann  made  a  similar  discovery  with  respect  to  the  animal 
body,  thus  laying  the  foundations  for  the  "  cell-theory."  The 
main  propositions  involved  in  the  cell-theory,  as  stated  by 
Professor  Thomson,  are,  first,  that  all  organisms  are  either 
built  up  of  single  cells  or  combinations  of  such  cells ;  second, 
that  all  organisms  begin  life  as  a  single  cell,  which,  in  the 
case  of  the  many-cell  organisms,  gives  rise  to  a  more  or  less 
complex  body ;  and  third,  that  the  function  of  a  multicellu- 
lar  organism  can  be  expressed  in  terms  of  the  activities  of 
its  component  cells.  Though  the  third  proposition  may  now 
require  some  modification,  the  cell-theory  proved  an  invalu- 
able unifying  conception  in  biology.  In  1846  the  word  "pro- 
toplasm," originally  used  in  a  different  sense,  was  applied  by 
von  Mohl  to  the  substance  inclosed  by  the  cell-wall  in  plants  ; 
and  in  1861  Max  Schultze  established  the  essential  identity  of 
protoplasm  with  the  life-substanoe  in  the  animal  cell,  which 
had  been  called  sarcode.  Embryology  was  broadened  through 
the  influence  of  von  Baer  (1792-1876),  who,  in  1827,  de- 
scribed the  primary  germ-layers  in  the  vertebrate  embryo.  We 
owe  the  appreciation  of  the  importance  of  the  embryological 
basis  of  classification  to  von  Baer. 

The  nineteenth  century  was  prolific  in  experiments  to  test 
whether  there  could  be  spontaneous  generation  of  organisms, 
and  a  war  of  discussion  was  waged  between  those  who  sup- 
ported the  idea  and  those  whose  experiments  seemed  to  show 
that  all  the  living  organisms  experimented  upon  came  from 
preexisting  life.  The  experiments  of  Francesco  Redi  (1626- 
1697)  in  the  seventeenth  century  had  shown  that  maggots 
did  not  appear  in  decaying  meat  if  flies  were  prevented  from 
having  access  to  it,  and  the  discussion  took  a  new  turn 
about  the  possibility  of  the  spontaneous  generation  of  the 
animalcules  (such  minute  animals  as  the  infusorians  and  roti- 
fers). Some  of  the  earlier  experimenters  did  not  succeed  in 


HISTORICAL  DEVELOPMENT  OF  ZOOLOGY     447 

reaching  the  truth  on  account  of  their  carelessness  in  opera- 
tion, but  it  was  finally  shown  that  no  animalcules  appeared 
in  water  which  had  been  boiled  thoroughly  and  sealed  so  that 
no  germs  could  enter.  The  final  conclusive  experiments 
were  those  of  Pasteur  (1822-1895)  about  1860,  and  those 
of  Tyndall  (1820- 
1893)  a  few  years 
later. 

An  important  step 
in  paleontology  was 
made  when  Boucher 
de  Perthes,  in  1836, 
found  flint  axes  in 
northern  France  so 
far  beneath  the  sur- 
face of  the  ground 
that  it  pointed  to- 
ward a  greater  an- 
tiquity for  man  than 
had  hitherto  been 
believed.  Though 
combated  by  many, 
the  truth  finally 

prevailed,     and 

,  FIG.  232.  Louis  Agassiz 

man  s   presence  in 

Europe  was  proven  at  least  as  far  back  as  glacial  times. 
Louis  Agassiz  (1807-1873,  Fig.  232)  is  famous  both  as  an 
investigator  along  many  different  lines  and  as  an  inspiring 
teacher.  He  was  born  in  Switzerland,  near  Lake  Neuchatel, 
and  after  study  in  Europe  came  to  America  at  the  height 
of  his  reputation  in  1846,  where  he  remained  during  the  rest 
of  his  life.  He  became  connected  with  Harvard  University 
in  1847,  and  the  Museum  of  Comparative  Zoology  at  Cam- 
bridge, Massachusetts,  is  a  monument  to  his  enthusiasm  and 


448  GENERAL  ZOOLOGY 

devotion.  Agassiz'  researches  cover  a  wide  field,  but  per- 
haps his  most  important  contribution  to  zoology  is  his  work 
on  fossil  fishes.  It  is  interesting  to  note  that  he  was  the  last 
great  zoologist  to  hold  out  against  the  evolutionary  views 
which  came  in  with  the  epoch-making  work  of  Charles 
Darwin. 

We  must  go  back  for  a  moment  to  consider  the  beginning 
of  the  evolutionary  views,  which,  as  we  have  said  on  page  101, 
are  accepted  in  some  form  by  practically  all  scientific  men 
to-day.  Professor  Osborn  in  the  volume  referred  to  in 
the  discussion  of  Buffon  says  that  the  Greek  philosopher 
Empedocles,  of  Agrigentum  (495-435  B.C.),  may  justly  be 
called  the  father  of  the  evolution  idea,  since  he  conceived  of 
animals  and  plants  as  arising  through  the  fortuitous  play  of 
the  great  forces  of  nature,  love  and  hate,  on  the  four  elements, 
fire,  water,  earth,  and  air.  First  appeared  the  plants;  later, 
after  many  trials,  the  animals,  —  the  latter  not  as  complete 
individuals  but  as  parts  of  individuals.  From  the  chance 
meeting  of  parts  came  monstrous  forms  incapable  of  propa- 
gation. After  ceaseless  trials  Nature  produced  the  fit  and 
perpetual  tribes.  Here  is  the  germ,  according  to  Professor 
Osborn,  of  the  survival  of  the  fittest  or  of  natural  selection. 

Aristotle's  conception  has  already  been  referred  to.  In  one 
form  or  another,  evolutionary  views  were  put  forward  by 
philosophers  and  naturalists  during  the  long  period  which 
intervened  between  Greek  thought  and  the  time  of  Buffon. 
These  views,  while  interesting  historically,  need  not  detain 
us  now,  nor  can  we  stop  to  outline  further  Buffon's  influence 
on  evolutionary  thought.  We  must  pass  at  once  to  the  great 
figure  of  Lamarck  (1744-1829).  We  have  already  mentioned 
(Chapter  X,  p.  108)  the  two  factors  of  evolution  with  which 
the  name  of  Lamarck  is  associated,  and  have  noted  the  fact 
that  Erasmus  Darwin  (1737-1802),  grandfather  of  Charles 
Darwin,  seems  to  have  anticipated  Lamarck's  views  in  part. 


HISTORICAL  DEVELOPMENT  OF  ZOOLOGY     449 

Lamarck's  four  propositions  are  as  follows  : 

First  Law.  Life  by  its  own  activities  tends  continually  to  increase 
the  volume  of  every  body  that  possesses  it,  and  to  increase  the  size  of 
all  the  parts  up  to  a  limit  which  it  itself  imposes. 

Second  Law.  The  production  of  a  new  organ  or  part  results  from  a 
new  need,  which  continues  to  be  felt,  and  from  the  new  movement  which 
this  need  originates  and 
sustains. 

Third  Law.  The  de- 
velopment of  organs  and 
their  power  of  action  are 
always  in  direct  relation 
to  the  employment  of 
these  organs. 

Fourth  Law.  All  that 
has  been  acquired  or 
changed  in  the  structure 
of  individuals  during 
their  life  is  preserved  by 
generation  and  trans- 
mitted to  new  individuals 
which  have  undergone 
these  changes. 

Discussion  of  the 
validity  of  these  prin- 
ciples still  continues. 

Though    Lamarck's 

.      PT  FIG.  233.   Charles  Darwin 

influence    can    be 

traced  in  his  contemporaries  and  those  who  followed  him,  it 
does  not  seem  that  he  directly  affected  the  far  more  important 
work  of  Darwin. 

Without  doubt  biology  owes  a  greater  debt  to  Charles 
Darwin  (1809-1882,  Fig.  233)  than  to  any  other  man.  He 
compelled  the  attention  of  men  in  a  way  and  to  an  extent 
unsurpassed  by  any  other  writer.  His  labors  were  directed 
not  alone  towards  stating  the  doctrine  of  descent  with 
modification  and  marshaling  evidence  to  its  support,  but 


450  GENERAL  ZOOLOGY 

he  promulgated  the  theory  of  natural  selection  as  the  main 
though  not  the  chief  factor  in  evolution.  His  work  was  a 
triumph  for  the  inductive  method,  for  never  before  had  such 
an  array  of  facts  been  collected  and  presented.  The  battle 
was  first  fought  over  the  fixity  of  species,  till  belief  in  that 
theory  no  longer  became  possible.  Then  investigators  sprung 
up  on  every  side,  stimulated  by  the  brilliancy  and  simplicity 
of  natural  selection  (to  which  Darwin  afterwards  added  sexual 
selection),  or  anxious  to  disprove  its  validity  as  a  factor  in 
evolution. 

When  twenty-two  years  of  age  Darwin  sailed  on  H.M.S. 
Beagle  on  a  voyage  to  South  America  and  around  the  world. 
He  returned  to  England,  his  interest  in  natural  history 
strengthened  and  the  problems  of  life  outlining  themselves 
to  him.  This  voyage  was  the  beginning  of  the  collection 
of  that  vast  store  of  facts  which  were  afterward  organized 
and  used  with  such  effect.  For  over  twenty  years  he  worked 
getting  together  facts  which  had  to  do  with  the  variation  of 
animals  and  plants,  and  thinking  on  the  general  problem. 
And  now  occurred  one  of  the  most  remarkable  coincidences  in 
the  whole  history  of  science.  While  Darwin  was  elaborating 
his  views  on  the  mutability  of  species  Alfred  Russel  Wallace 
(born  1822),  an  English  naturalist  then  in  the  Malay  Archi- 
pelago, arrived  at  practically  the  same  conclusion  that  Dar- 
win had  reached.  By  the  aid  of  friends  it  was  arranged  that 
publication  should  be  simultaneously  made,  and  therefore  in 
the  Journal  of  the  Linncean  Society  of  London  of  June  30, 
1858,  we  find  two  papers  of  transcendent  interest.  The  one 
by  Darwin  consists  of  portions  of  manuscript  written  in  1839 
and  1844,  entitled  On  the  Variation  of  Organic  Beings  in  a 
State  of  Nature;  on  the  Natural  Means  of  Selection ;  on  the 
Comparison  of  Domestic  Races  and  True  Species.  Wallace's 
paper  is  On  the  Tendency  of  Varieties  to  depart  indefinitely 
from  the  Original  Type.  A  year  afterward  appeared  Darwin's 


HISTORICAL  DEVELOPMENT  OF  ZOOLOGY     451 

Origin  of  Species,  in  which  the  theory  of  natural  selection  was 
elaborated.  The  main  features  of  the  theory  have  already 
been  outlined  in  Chapter  X.  Darwin  was  a  prolific  writer; 
some  of  his  books  are  On  the  Variations  of  Animals  and  Plants 
under  Domestication,  The  Descent  of  Man,  and  The  Expres- 
sions of  the  Emotions  in  Man  and  the  Lower  Animals.  In  all 
of  these  natural  selection  is  applied. 

Among  the  contemporaries  who  aided  Darwin  in  his  work, 
and  who  were  in  turn  influenced  by  him,  may  be  mentioned 
the  names  of  Herbert  Spencer  (1820-1903),  the  philosopher 
and  author  of  the  Principles  of  Biology;  Ernst  Haeckel  (born 
1834),  the  brilliant  author  of  General  Morphology  ;  Thomas 
H.  Huxley  (1825—1895),  a  great  teacher  and  popularize!1  of 
zoology,  and  author  of  important  works ;  and,  finally,  August 
Weismann  (born  1834),  who  aroused  skepticism  as  to  the 
hereditary  transmission  of  acquired  characters,  and  who  has 
made  important  supplementary  contributions  to  the  theory 
of  natural  selection. 

It  is  impossible  to  overestimate  the  influence  of  the  selec- 
tion theory  in  the  progress  of  modern  zoology.  It  has  thrown 
new  light  on  all  fields  of  activity,  so  that  it  may  be  said  that 
a  new  science  of  zoology  has  arisen.  The  importance  of  care- 
ful experiment  has  been  appreciated  as  never  before.  A  host 
of  investigators  have  sprung  up,  whom  to  merely  mention 
would  transcend  the  limits  of  this  work.  The  work  of  a  very 
few  men  has  been  referred  to  in  the  preceding  chapters,  in  the 
effort  to  give  some  picture  of  the  state  of  the  science  of 
zoology  to-day.  Everywhere  zoologists  are  endeavoring  to 
learn  the  truth  about  animals,  trying  to  understand  better 
the  problem  of  animal  life,  and  the  greatest  problem  of  all, 
towards  which  the  solution  of  all  others  is  directed,  — the 
problem  of  man  and  his  relation  to  the  universe. 


INDEX 


Abomasum,  417 

Aboral  surface,  236 

Absorption,  200 

Acephala,  175 

Acquired  characters,  inheritance  of, 
107 

Actinozoa,  260 

Adhesive  papillae,  303 

Adrenal  capsules,  403 

Aftershaft,  366 

AGASSIZ,  ALEXANDER,  on  formation 
of  coral  islands,  262  ;  on  habits  of 
basket-fish,  245 

AGASSIZ,  MRS.  E.  C.,  on  habits  of 
basket-fish,  245 

AGASSIZ,  Louis,  447 

Age  of  Amphibians,  345,  346,  361 ; 
of  Coal  Plants,  345,  346,  361 ;  of 
Fishes,  324 ;  of  Invertebrates,  295, 
324;  of  Mammals,  428,  431;  of 
Man,  431,  433,  434  ;  of  Reptiles, 
360,  362,  396,  410,  428 

Aggressive  resemblance,  23 

Albatross,  wandering,  376 

Albinism,  407    . 

Alder-blight,  34 

Alligators,  359 

Alluring  coloration,  24 

Alternation  of  generations,  267 

Amblystoma,  340 

Amoeba,  280 

Amoebocytes,  207 

Arncebulae,  284 

Amphibians,  age  of,  345,  346,  361 ; 
definition  of,  339 ;  geological  de- 
velopment of,  345 

Ampullae,  239,  273 

Analogy,  130 

Anatomy,  comparative,  436 

ANDERSON,  DR.  J.,  on  colors  of 
mantids,  24 

Annelida,  225 

Annulata,  225,  298 

Annulus,  135 

Ant-eater,  spiny,  408 


Antelopes,  413,  416  ;  pronghorn, 
414 

Antennae,  2,  127 

Antennule,  127 

Antlers,  415 

Ants,  78;  agricultural,  81;  corn- 
louse,  79;  honey,  80 

Anura,  343 

Apes,  423 

Aphids,  33,  104 ;  woolly,  34 

Appendix  vermiformis,  403 

Arachnida,  122,  156 

Archaean  Time,  293 

Archaeopteryx,  396 

Archenteron,  216 

ARISTOTLE,  437 

Armadillos,  411 

Artemia,  148 

Arthropoda,  156,  299 

Assimilation,  202 

Asteroidea,  251 

Asymmetry,  187 

Atoll,  262 

Atrial  pore,  302 

Atrium,  301 

Aves,  374 

Axolotl,  341 

Baboon,  Cape,  427 
Back-swimmers,  31 
BACON,  FRANCIS,  438 
BACON,  ROGER,  438 
BAER,  KARL  ERNST  VON,  446 
Barbs,  366 
Barbules,  366 
Barnacles,  150,  153 
Basipodite,  130 
Basket-fish,  244 
BATESON,  WILLIAM,  110 
Bats,  422,  431 ;  vampire,  423 
Beadsnake,  355 
Bear,  420,  434 
Beaver,  418,  419 

Bees,  guest,  76  ;  honey,  72 ;  leaf-cut- 
ter, 78;  solitary,  77 


453 


454 


GENERAL  ZOOLOGY 


Beetles,  45 ;  bombardier,  38 ;  click, 
41 ;  diving,  39 ;  ground,  37 ;  June, 
44 ;  lady,  40 ;  May,  44 ;  scavenger, 
40;  stag,  106;  tiger,  37;  water, 
38;  whirligig,  38 

Biological  Survey,  392 

Biology,  101,  436 

Bionomics,  436 

Bird  Day,  396 

Birds,  definition  of,  374 ;  diving,  375; 
economic  importance  of,  392  ;  gal- 
linaceous, 381 ;  geological  devel- 
opment of,  396;  migration  of, 
390  ;  mocking,  395  ;  of  prey,  383  ; 
perching,  386;  shore,  380;  sing- 
ing, 386 

Blackbird,  crow,  394 

Blacksnake,  357 

Blastopore,  216 

Blasts,  286 

Blastula,  214,  244 

Bluebird,  390 

Blue  jay,  389 

Bob-white,  382 

BOJANUS,  PKOFESSOR,  on  nephridia 
of  mollusks,  161 

Botany,  436 

BOUCHER  DE  PERTHES,  447 

Bovidse,  416 

Brachiopoda,  234 

Brachiopods,  233,  296,  347 

BROOKS,  PROFESSOR,  on  early  stages 
of  oyster,  167  ;  on  environment  of 
oyster,  168 

BROWN-SEQUARD,  on  guinea-pigs, 
108 

Bryozoa,  233 

Budding,  258 

BUFFON,  444 

Bugs,  36;  squash,  31;  plant,  31; 
water,  30 

Bumblebees,  75 

BUMPCS,  PROFESSOR  H.  C.,  on  egg- 
laying  of  lobster,  142 

Bureau  of  Animal  Industry,  work 
of,  230 

Bureau  of  Fisheries,  work  of,  322 

Bursa  copulatrix,  12 

Butterfly,  milkweed,  46;  monarch, 
46  ;  swallow-tail,  49  ;  viceroy,  48  ; 
White  Mountain,  48 

Buzzard,  turkey,  384 

Byssus,  164 


Caddice-flies,  105 

Cseca,  intestinal,  241 ;  pyloric,  240 

Caecum,  403 

CALKINS,  PROFESSOR  G.  N.,  on  ex- 
periments with  rejuvenescence  in 
Paramcecium,  290 

Camels,  413,  416 

Canal,  radial,  239,  268;  ring,  239; 
stone,  239 ;  excurrent,  274  ;  incur- 
rent,  273. 

Canidse,  420 

Canines,  414 

Capillaries,  202 

Caprella,  147 

Carapace,  125 

Carbohydrates,  198 

Carboniferous  Age,  345,  346,  361 

Carnivora,  420 

Cassowaries,  374 

CASTLE,  PROFESSOR  W.  E.,  on  Men- 
del's law,  113 

Cats,  420,  425 ;  caff  re,  420 ;  Egyptian, 
420 ;  saber-toothed,  431 

Cavity,  gastrovascular,  256 ;  mantle, 
159 

Cells,  collar,  273;  polar,  213;  pole, 
216 ;  wandering,  274 

Cement,  401 

Centipeds,  122 

Centrosomes,  211 

Cephalopoda,  193,  194 

Cephalothorax,  125 

Cerata,  186 

Ceratosaurus,  361 

Cervidae,  416 

Cestoda,  229 

Cetacea,  412 

Chsetopoda,  225 

Chameleons,  353 

Cheliped,  128 

Chelonia,  357 

Chimpanzee,  424 

Chiroptera,  422 

Chitin,  2 

Chromosomes,  114,  211 

Chrysalis,  47 

Cicadas,  32;  periodical,  32 

Cilia,  207,  287 

Circulation,  201 

Clam,  long-neck,  157 ;  soft-shell, 
157 

Cleavage  spindle,  214 

Clitellum,  196 


INDEX 


455 


Cochineal  insects,  36 

Cockatoos,  384 

Cockroaches,  2*0,  100 

Cocoon,  51 

Ccelentera,  271,  297 

Coleoptera,  43 

Colleterial  gland,  12 

Colloids,  199 

Coloration,  alluring,  24 ;  warning, 
40 

Columbse,  382 

Comb-jelly,  270 

Comrnensalism,  79 

Commissure,  cerebral,  163 

Conchologists,  185 

Conjugation,  289 

Connectives,  cerebro-visceral,  163 

Coral  islands,  261  ;  polyp,  259 

Corallite,  260 

Corals,  296,  347 

Corvidee,  389 

Cow,  413,  416 

Cow-bird,  389 

Coxopodite,  130 

Crabs,  blue,  145;  fiddler,  146;  her- 
mit, 143;  horseshoe,  154;  spider, 
144 

Cranes,  380,  391,  397 

Crinoidea,  251 

Crinoids,  246,  296,  347 

Crocodiles,  359 

Crop,  198,  367 

Crow,  389,  393 

Crustacea,  152,  156 

Crustaceans,  parasitic,  150,  153 

Crystalline  style,  160 

Crystalloids,  199 

Ctenophora,  271 

Cuckoos,  395 

CUNNINGHAM,  PROFESSOR,  on  color 
of  flounders,  321 

CUVIER,  GEORGES,  445 

Cyclops,  149,  153,  263 

Cytoplasm,  211,  281 

DANA,  PROFESSOR  J.  D.,  on  forma- 
tion of  coral  islands,  262  ;  on  geo- 
logical distribution  of  animals,  363 

DARWIN,  CHARLES,  449;  on  forma- 
tion of  coral  islands,  262 ;  on 
habits  of  earthworms,  220;  on 
natural  selection,  102  ;  on.  pigeons, 
373;  on  sexual  selection,  106 


DARWIN,  ERASMUS,  108,  448 

DEAN,  PROFESSOR  B.,  on  evolution  of 
fishes,  316 ;  on  habits  of  Nautilus, 
192 

Deer,  413,  415,  416 

Degeneration,  98 

Dentine,  400 

Dermal  pores,  273 

DE  VARIGNY,  on  evolution,  109 

Devonian  Period,  324 

DE  VRIES,  HUGO,  on  the  mutation 
theory,  110 

Diaphragm,  403 

Diastase,  199 

Differentiation,  216,  297 

Dimorphism,  49 

Dinosaurs,  361 

Dipnoans,  321 

Diptera,  64,  100 

Direct  influence  of  environment,  108 

Discontinuous  distribution,  323 

Distribution,  geographical,  436;  geo- 
logical, 436 

Dogs,  420,  425 

Dolphins,  412 

Doves,  382 ;  rock,  364  ;  wild,  382 

Dragon-flies,  27 

Drones,  72 

Duckbill,  408 

Ducks,  378,  391  ;  canvasback,  378  ; 
mallard,  378  ;  domestic,  378 

Eagle,  383 

Earthworm,  297 

Echeneis,  357 

Echinoderma,  251,  298 

Echinoidea,  251 

Ecology,  animal,  436 

Ectoderm,  215,  264 

Ectoplasm,  281 

Edentates,  411,  433 

Eels,  319 

Egg,  209 

Egrets,  379 

EIGENMANN,    PROFESSOR,    on    blind 

crayfishes,  136 
Elasmobranchii,  317 
Elephants,  413,  414;  African,  417  ; 

Asiatic,   417 
Embryo,  214 
Embryology,  130 
EMPEDOCLES,  448 
Emus,  374 


456 


GENERAL  ZOOLOGY 


Enamel,  401 

Endoderm,  215,  264 

Endoplasm,  281 

Endopodite,  130 

Energy,  204 

ENTEMAN,    DR.,    on     paper-making 

wasps,  66 
Entomology,  84 
Environment,    direct    influence    of, 

108 

Enzymes,  199 
Epiglottis,  404 
Epipharynx,  6 
Epiphragrn,  182 
Epithelium,  174 
Epoch,  Glacial,  392,  431 
Era   of  the   ancient   forms   of   life, 

346;  of  the  mediaeval  forms  of  life, 

360 

Erosion  theory,  262 
Etiology,  436 
Euglena,  283 
Evolution,  101 
Excretion,  206 
^Exopodite,  130 
Exoskeleton,  84 

FABRE,  M.,  on  instinctive  acts  of 
Sphex,  88 

Facets,  2 

Family,  96 

Fat-bodies,  334 

Fats,  198 

Fatty  acids,  200 

Fauna,  93 

Fauna  areas,  94 

Feathers,  contour,  366  ;  down,  366 

Felidse,  420 

Femur,  3,  333 

Ferments,  199 

Fertilization,  213 

Filoplume,  366 

Finches,  389 . 

Fireflies,  43 

Fishes,  Age  of,  324  ;  bony,  317  ;  deep- 
sea,  323  ;  definition  of,  316  ;  eco- 
nomic importance  of,  322 ;  geo- 
graphical distribution  of,  322  ; 
geological  development  of,  324 ; 
lung,  321,  325,  347 ;  sucking,  357 

Flagella,  273 

Flatfishes,  320 

Flatworm,  225 


Flies,  blow,  59 ;  bot,  60 ;  bluebottle,  59 ; 

house,  58, 104 ;  hover,  61 ;  tsetse,  60 
Flounders,  320 
FLOWER  and  LYDEKKER,  on  whales, 

412 

Flycatchers,  388,  395 
Fowl,  domestic,  381  ;  jungle,  381 
Fox,  420 
Fringillidse,  389 
Frogs,  343  ;  bull,  327  ;  green,  327 

GALEN,  439,  442 

Gall-flies,  81  ;  guest,  81  ;  oak,  81 

Gallinse,  381 

GALVANI,  445 

Ganglia,  cerebro-pleural,  163 

Ganglion,  pedal,  163  ;  visceral,  163 

GANONG,  PROFESSOR  W.  F.,  on  form 
of  sea-urchins,  247 

Garpike,  318,  325,  347 

Gasteropoda,  187,  194 

Gastrula,  215,  244 

Geese,  378 

Gemmules,  276 

Generalized  forms,  98 

Generation,  spontaneous,  439 

Genus,  95 

Geological  development  of  amphibi- 
ans, 345 ;  of  birds,  396  ;  of  fishes, 
324 ;  of  insects,  99 ;  of  inverte- 
brates, 295  ;  of  mammals,  428 

Germinal  spot,  211 

Germ-layers,  216 

GESNER,  KONRAD  VON,  442 

Gibbon,  426 

Gill-bailer,  128 

Gill-chamber,  128 

Gill-slits,  301 

Giraffe,  413 

Glacial  Epoch,  392,  431 

Gland,  foot,  179  ;  green,  134  ;  cal- 
ciferous,  198 

Glochidium,  172 

Glycerin,  200 

Glycogen,  204 

Goat,  413,  415,  416 

Gorilla,  424,  426 

Grasshoppers,  18 

GRASSI,  PROFESSOR,  on  life-history 
of  malarial  parasite,  286 

Grouse,  ruffed,  382 

Guinea-pig,  418 

Gulls,  376,  383 


INDEX 


457 


HAECKEL,  ERNST,  451 
Haeniocyanin,  102 

Haemoglobin,  102,  203 

Halibut,  320 

Hares,  418  ;  varying,  419 

Harvest-flies,  32 

Harvestmen,  121 

HARVEY,  WILLIAM,  442 

Hawks,  383,  391  ;  chicken,  383  ; 
cooper,  393  ;  hen,  383  ;  red- 
shouldered,  383  ;  red-tailed,  383, 
400  ;  sharp-shinned,  393 

HAY,  DR.  O.  P.,  on  blind  crayfishes, 
136 

Hemiptera,  30,  99,  100 

Heredity,  102,  112  ;  Mendel's  law 
of,  112 

Hermaphrodite,  170 

Herod iones,  379 

Herons,  379  ;  great  blue,  380 

HERRICK,  PROFESSOR  F.  H.,  on  egg- 
laying  of  lobster,  143 

Hexapoda,  84,  150 

Hinge-ligament,  157 

Hippopotami,  413 

Hirudinea,  225 

Holothuroidea,  251 

Homing  faculty,  373 

Ilomology,  130 

Honeydew,  34 

Hornets,  68 

Horse,  domestic,  413,  410,.  417,  428, 
431 

HOWARD,  DR.  L.  O.,  on  the  gypsy 
moth,  90 

HUXLEY,  THOMAS  H.,  451 

Hysenidse,  420 

Hybrids,  96 

Hydra,  296  ;  brown,  263  ;  green,  263 

Hydroids,  265 

Hydrozoa,  267 

Hyenas,  420,  434 

Hyla,  338,  343,  344 

Hymenoptera,  83,  100 

Hypopharynx,  6 

Ichneumon-flies,  82 
Ichthyologists,  326 
Icteridse,  389 
Iguana,  Mexican,  353 
Imago,  14 
Incisors,  399 
Infusoria,  291 


Insectivora,  422 

Insects,  347  ;  instinct  and  intelligence 
in,  85 

Invertebrate  phyla  and  classes,  299  ; 

Invertebrates,  Age  of,  295,  324  ;  evo- 
lution of,  292 

Jackals,  421 

Jaguar,  420 

JAMESON,  PROFESSOR  H.  L.,  on  life- 
history  of  trematode  worm,  227;  on 
the  formation  of  pearls,  173 

Jay,  389 

Jellyfish,  267 

JENNINGS,  PROFESSOR  H.  S.,on  loco- 
motion of  amoeba,  281 ;  on  activi- 
ties of  Protozoa,  291 

JORDAN,  PROFESSOR,  on  rapid  devel- 
opment of  the  house-fly,  104 

JUDD,  DR.,  on  food  of  birds,  393 

Labium,  2 

Labrum,  2 

Labyrinthodonts,  346 

Lacertilia,  351 

Lac-insect,  36 

Lacteals,  404 

LAMARCK,  107,  448 

Lamellibranchia,  175 

LANCASTER,  PROFESSOR  E.  RAY,  on 
bionomics,  436 

Lancelet,  301 

Lark,  meadow,  395 

Larva,  36 

Lateral  line,  306 

Leech,  224 

Leopard,  420 

Lepidoptera,  57,  100 

Lice,  fish,  150  ;  plant,  33 

Limicolse,  380 

LINNJEUS,  96,  443 

Lion,  420,  434 

Lizards,  351  ;  legless,  352 ;  flying, 
362  ;  pine,  348 

Lobster,  138 

Locusts,  15  ;  common  red-legged,  1  ; 
lesser,  1,  16;  Rocky  Mountain,  1, 
15,  93;  seventeen-year,  32;  thir- 
teen-year, 32 

LOEH,  PROFESSOR  JACQUES,  on  artifi- 
cial parthenogenesis,  290 

Longipennes,  376 

Loon,  375 


458 


GENERAL  ZOOLOGY 


Lophophore,  232,  233 
Lymph-hearts,  331 
Lynx,  420 

Macronucleus,  288 

Madreporic  body,  239 

Maggots,  59 

Malarial  parasite,  284 

MALPIGHI,  443 

Malpighian  tubes,  8 

Mammals,  Age  of,  428,  431  ;  carniv- 
orous, 420  ;  definition  of,  408  ;  eco- 
nomic importance  of,  427  ;  flesh- 
eating,  420,  431 ;  gnawing,  418  ; 
hoofed,  413,  416,  431,  434  ;  insect- 
eating,  422,  431 ;  instinct  and  in- 
telligence in,  425 

Mammary  glands,  405 

Mammoth,  433 

Man,  423,  424;  Age  of,  431,  433, 
434  ;  races  of,  425 

Manna,  36 

Mantids,  22 

Mantle,  159 

Mantle-fold,  159 

Manubrium,  266 

Many  plies,  417 

Marsupials,  409,  434 

Mastigophora,  291 

Mastodon,  433 

Maturation,  211 

MAUPAS,  on  conjugation  in  Paramce- 
cium,  289 

Maxillae,  2,  116,  127 

Maxilliped,  127 

May-flies,  25,  98 

MEAD,  PROFESSOR,  on  food-getting 
habits  of  starfish,  241 

Measuring-worm,  57 

Medusae,  265 

Melanism,  407 

Melanoplus,  95 

MENDEL,  GREGOR,  113 

Mendel's  law,  112 

Mesenteries,  255 

Mesoderm,  215 

Mesoglcea,  279 

Mesothorax,  3 

Mesozoic  Time,  360 

Mesozoic  upheaval,  363 

Metabolism,  206 

Metamerism,  235 

Metamorphosis,  27 


Metathorax,  3 

Metazoa,  298 

Method,  inductive,  437 

Mice,  418 

Micronucleus,  288 

Middle  Ages,  440 

Migration  of  birds,  390 

Millepeds,  124 

Milt,  155 

Mimicry,  protective,  48 

Mites,  121 

MITRA,   PROFESSOR,  on    function  of 

crystalline  style,  160 
Mniotiltidse,  388 
MO'BIUS,      PROFESSOR,    on     oyster's 

chances  of  living,  169 
Mocking-bird,  395 
MOHAMMED,  440 
MOHL,  HUGO  VON,  446 
Molars,  400 
Mole,  star-nosed,  422 
Mollusca,  194,  299 
Molluscoida,  234,  298 
Mollusks,  296 
Molting,  140 

Monkeys,  423,  426,  427  ;  spider,  423 
Monotrernata,  408 
MOORE,  PROFESSOR,  on  coloration  of 

leech,  225 
MORGAN,  PROFESSOR  C.   LLOYD,  on 

instinct   and   intelligence,   85  ;  on 

intelligence  of  mammals,  426  ;  on 

rational  acts,  87 
MORGAN,  PROFESSOR  THOMAS  HUNT, 

on  mutation  theory,  111 
Morphology,  98,  130,  436 
MORSE,  PROFESSOR  E.  S.,  on  habits 

of  brachiopods,  233 
Mosquito,  61,  284 
Mother  Carey's  chickens,  376 
Mother-of-pearl,  166 
Moths,  51  ;  American  silkworm,  52  ; 

Chinese  silkworm,  51  ;  gypsy,  89  ; 

hawk,   53;   regal,    56;   silkworm, 

51  ;  sphinx,  53  ;  tussock,  55  ;  un- 

derwing,  53  ;  vaporer,  56 
Mucus,  179 
MURRAY,  DR.  JOHN,  on  formation  of 

coral  islands,  262 
Mussel,  171 
Mutation  theory,  110 
Myriapoda,  124,  156 
My  sis,  153 


\ __ 


INDEX 


459 


Nacreous  layer,  159 
Narwhal,  418 
Nauplius,  152 
Nautiloids,  193 
Nautilus,  191 
Nebular  hypothesis,  293 
Nemathelminthes,  230,  298 
Neinatoda,  230 
Nephridia,  161,  206 
Nerve  control,  207 
Nerve-cell,  motor,  208  ;  sensory,  208 
Nerve-cord,  303 

Nervous  system,  central,  208 ;  periph- 
eral, 208 
Nettle-cells,  258 
Nettling-capsules,  252 
Newts,  339,  342 
Nitrogenous  waste,  162 
Notochord,  302 
Nototrerna,  344 
Nucleoplasm,  281 
Nucleus,  211,  281 
Nudibranch,  186 
Nymph,  13 

Odonata,  29,  99,  100 

Operculum,  185,  306,  334 

Ophidia,  353 

Ophiuroidea,  251 

Opossums,  409,  410  ;  Virginian,  410 

Oral  surface,  236 

Orang-utan,  423,  426 

Orders,  97 

Organs,  of  Bojanus,  161 ;  terrifying, 
42 

Orioles,  389  ;  orchard,  395 

Ornithologists,  391 

Orthoceras,  367 

Orthoptera,  24,  99,  100 

OSBORN,  PROFESSOR,  on  Linnaeus  and 
Buffon,  444  ;  on  Empedocles,  448 

Oscula,  273 

Osmosis,  200 

Osphradium,  184 

Ostia,  257 

Ostrich,  African,  374  ;  South  Ameri- 
can, 374 

Otocyst,  127 

Otoliths,  310 

Oviduct,  210 

Oviparous,  316 

Owls,  383,  386  ;  great  horned,  393 

Oxen,  413,  415,  416 


Oxidation,  203 

Oyster,  165  ;  -beds,  186  ;  -drill,  184  ; 
-farm,  167  ;  fry,  167  ;  pearl,  173 

Palate,  soft,  401 ;  hard,  403 

Paleontologists,  193 

Paleontology,  436 

Paleozoic  Time,  346 

Paramcecium,  286 

Parasites,  60 

PARKER,  PROFESSOR  G.  H.,  on  feed- 
ing habits  of  sea-anemone,  254 

PARKER  and  HASWELL,  on  birds, 
373  ;  on  classification,  298 

Parrots,  397  ;  gray,  384 

Parthenogenesis,  34 ;  artificial,  290 

Partridge,  382 

Passeres,  386 

PASTEUR,  447 

Paunch,  417 

Pearls,  formation  of,  173 

PECKHAM,  DR.  and  MRS.,  on  the 
digger-wasp,  70 ;  on  instinctive 
acts  in  wasps,  86 ;  on  jumping- 
spiders,  120 

Pedicellarise,  238 

Peduncle,  233 

Pelecypoda,  175,  194 

Pelican,  white,  377 

Peptone,  200 

Perch,  yellow,  305 

Perching  birds,  386 

Pericardial  sinus,  133 

Pericardium,  159 

Periwinkle,  185 

Petrels,  stormy,  376 

Phagocytes,  85 

Pheasants.  381 

Phyla,  97 

Phylloxera,  34 

Physiological  processes,  196 

Physiology,  comparative,  431 

Pici,  385 

Pigeons,  carrier,  373  ;  domestic,  364  ; 
fantail,  373  ;  passenger,  382  ; 
pouter,  373  ;  tumbler,  372,  373 

Pigs,  413 

Pill-bug,  147 

Pinnae,  398 

Pisces,  316 

Platyhelminthes,  229,  298 

Plectoptera,  26,  99,  100 

PLINY.  440 


460 


GENERAL  ZOOLOGY 


Plovers,  380  ;  golden,  391  ;  upland, 

381 

Plowshare  bone,  370 
Plumatella,  231 
Polian  vesicles,  243 
Pollination,  1)1 
Polymorphism,  49 
Polyp,  252  ;  fresh-water,  203 
Polyzoa,  233 
Porcupine,  418,  419 
Porifera,  278,  297 
Porpoise,  412 
POTTS,    PROFESSOR,    on     habits     of 

sponge,  276 
POULTON,  PROFE.SSOR,  on  the  vaporer- 

moth,  56 
Prawn,  142 
Premolars,  400 
Primates,  423 
Prismatic  layer,  159 
Proboscidea,  416 
Proboscis,  46,  304 
Procyonidse,  420 
Pronuba,  92 
Prostomium,  196 
Protective  mimicry,  48 
Protective  resemblance,  18 
Proteids,  198 
Prothorax,  3 

Protoplasm,  202,  205,  211,  280 
Protopodite,  1::10 
Protorohippus,  428 
Protozoa,  291 
Psalterium,  417 
Pseudopodia,  280 
Psittaci,  384 

Psychology,  comparative,  436 
Pterosaurs,  362 
Pulp-cavity,  400 
Pulvillus,  4 
Puma,  420 
Pupa,  36 
Pygopodes,  375 

Quail,  381,  382,  395 

Quaternary  Period,  431,  433,  434 

Rabbit,    cottontail,    419;     domestic, 

419;  gray,  419;  jack,  419 
"Raccoon,  420 
Rachis,  366 
Raptores,  383 


Rasping-tongue,  169,  177 

Rational  acts,  87 

Hats,  418 

Rattlesnake,  354,  355 

RAY,  JOHN,  443 

Rays,  317,  347 

RE DI,  FRANCESCO,  446 

Reef,  barrier,  262;  fringing,  262; 
coral,  261 

Reflex  action,  208 

Regeneration,  244 

Rejuvenescence,  289 

Repellent  odors,  32 

Reproduction,  by  artificial  parthe- 
nogenesis, 290  ;  by  budding,  258  ; 
by  conjugation,  289;  by  eggs  and 
spermatozoa,  209 :  by  equal  divi- 
sion, 282,  288  ;  by  gemmules,  276; 
by  parthenogenesis,  34  ;  by  spores, 
284  ;  by  statoblasts,  233 

Reptiles,  Age  of,  360,  362,  396,  410, 
428 ;  definition  of,  351  ;  geological 
development  of,  360 

Resemblance,  protective,  18 

Respiration,  203 

Reticulum,  417 

Rheas,  374 

Rhinoceros,  413,  414,  416,  434 

Rhinoderma,  343 

Robin,  American,  390 

Rodents,  418,  431 

Ross,  DR.  ,  on  life-history  of  malarial 
parasites,  286 

Rostrum,  127 

Rotifer,  230 

Rotifera,  231 

Rumen,  417 

Ruminants,  417 

RYDER,  PROFESSOR,  on  environment 
of  oyster,  168 

Salamanders,     339;     Alpine,     342; 
blunt-nose,  340 ;  Texan  cave,  340 
Salmon,  Atlantic,  320 
Sandpipers,  380 
Sand  worm,  222 
Saponification,  200 
Sapsucker,  385,  393 
Sarcodina,  291 
Saw-flies,  82 

Scale-insects,  35,  98 ;  San  Jose,  41 
Scallop,  169 
Scarabs,  44 


INDEX 


461 


SCHIEMENZ,  PROFESSOR,  on  food-get- 
ting habits  of  starfish,  241 

SCHLEIDEN,  M.  K.,  445 

SCHULTZE,  MAX,  446 

SCHWANN,  THEODOK,  446 

Scorpions,  121 

SCUDDER,  H.  S.,  on  the  distribution 
of  the  monarch  butterfly,  47 

Scyphozoa,  270 

Sea-anemone,  240;  -lily,  246,  296, 
347  ;  -squirt,  302  ;  -urchin,  247  ; 
-walnut,  270 

Seal,  Alaskan  fur,  421 

Selection,  artificial,  102 ;  natural, 
102;  sexual,  106 

Seminal  receptacles,  209 ;  vesicles, 
209 

SEMPER,  KARL,  on  the  pond-snail, 
109 

Serpula,  224 

Shark,  317,  325,  347 

Sheep,  413,  415,  416 

Shell-fish,  169 

Sieve-plate,  239 

Siphon,  160 

Siphonoglyphe,  254 

Siphuncle,  191 

Skate,  317 

Skipper,  50 

Skunk,  421 

Slipper-animalcule,  286 

Sloth,  412 

Slug,  garden,  182 

Snail,  land,  181 ;  pond,  177 

Snakes,  353  ;  copperhead,  355  ;  green, 
357 ;  water,  357 

Snipe,  Wilson's,  381 

Somites,  2 

Sow-bug,  147 

Sparrows,  389 ;  chipping,  395 ;  Eng- 
lish, 389,  393;  grasshopper,  395 ; 
house,  389  ;  song,  390 

Specialized  forms,  89 

Species,  95 

SPENCER,  HERBERT,  451 

Spermatozoon,  209 

Spicules,  275 

Spiders,  116;  garden,  117  ;  jumping, 
120;  trap-door,  120 

Spinal  cord,  302 

Spinnerets,  116 

Sponges,  296;  bath,  277;  fresh- 
water, 273 


Spores,  284 

Sporozoa,  291 

Spring-tails,  97 

Squame,  127 

Squid,  188 

Squirrels,  418,  419;  gray,  398;  red, 

405 

Statoblasts,  233 
Steapsiu,  199 
Stork,  white,  380 
Struthiones,  374 
Sturgeon,  318 
Subimago,  26 
Subsidence  theory,  262 
Sucking-disk,  188,  239 
Sunfishes,  321 
Swallow,  391,  395,  397 
Swan,  trumpeter,  378 
Swimmeret,  128 
Sycon,  277 
Symbiosis,  79 
Symmetry,    bilateral,    152;    radial, 

236,  298 
System,  water-vascular,  239 

Tadpole,  334 

Tapeworm,  227 

Tarantula,  119 

Tarsus,  4 

Teleostomi,  317 

Telson,  128 

Terns,  376 

Terrifying  organs,  42 

Theromorphs,  361 

THOMSON,  PROFESSOR,  on  the  cell 
theory,  446  ;  on  rapid  development 
of  aphis,  104 

Thoracic  duc£,  404 

TIIORNDIKE,  PROFESSOR,  on  intelli- 
gence of  animals,  426,  427 

Thrushes,  390 

Thymus  gland,  404 

Thyroid  gland,  404 

Thysanura,  97,  99 

Tibia,  4,  333 

Ticks,  121 

Tiedemann's  vesicle,  243 

Tiger,  420 

Toads,  343;  common,  344;  obstet- 
rical, 343 ;  Surinam,  343 

Tobacco-worm,  54 

Tonsils,  403 

Torpedoes,  317 


462 


GENERAL  ZOOLOGY 


Tortoises,  357;  box,  35*8;  painted,  359 
Tracheal  gills,  25 
Tree-frogs,  344 ;  Brazilian,  343 
Tree-toads,  344     . 
Trematoda,  227,  229 
Trematode,  174,  226 
Triceratops,  361 
Trichina,  229 
Trilobites,  153,  296,  347 
Trocheiniintb.es,  231,  298 
Trypsin,  199 
Tube-feet,  239 
Tubinares,  376 
Tunicata,  303 
Turbellaria,  226,  229 
Turdidse,  390 
Turkey-buzzard,  384 
Turkeys,  381 

Turtles,    357 ;    green,    357 ;    hawk- 
bill,  357 

TYNDALL,  JOHN,  447 
Tyrannidse,  388 

Umbo,  157 

Ungulates,  413,  431,  434  ;  even-toed, 

416;  odd-toed,  416 
Urethra,  404 
Uric  acid,  162 
Urodela,  339 
Urostyle,  331 
Ursidse,  420 
Uterus,  405 

Vacuoles,  contractile,  282,  288 
Vacuoles,  food,  287 
Vane,  366 
Varieties,  96 
Venues,  234 
Vertebrates,  292,  301 
VESALIUS,  ANDREAS,  441 
Vireos,  388,  389,   395;   white-eyed, 
389 


VON  BAER'S  law,  100 
Vultures,  383  ;  black,  384 

Walking-leaves,  22 ;  -sticks,  22 

WALLACE,  ALFRED  RUSSEL,  102,  450 

Warblers,  wood,  388,  395 

Warning  coloration,  40 

Wasps,  digger,  69 ;  mud-dauber,  69 ; 
social,  65 ;  solitary,  68 

Water-boatmen,  30 

Water-moccasin,  355 

Weevils,  90  ;  cotton-boll,  90 

WEISMANN,  AUGUST,  451 

Whale,  sperm,  413;  whalebone,  413 

Whip-scorpion,  122 

WHITE,  GILBERT,  444 

WILLEY,  PROFESSOR,  on  habits  of 
Nautilus,  192 

Wolves,  420 

Woodchuck,  418 

Woodcock,  381 

Woodpeckers,  385,  395,  397  ;  golden- 
winged,  385;  sap-sucking,  385, 
393;  three-toed,  385;  yellow-bel- 
lied, 385 

Worm,  acorn-tongue,  304  ;  tube,  224 

Wren,  house,  395 

AVRIGHT,  PROFESSOR  R.  RAMSAY,  on 
intelligence  of  monkeys,  426 

Xiphosura,154 

Zoea,  153 

Zooid,  231 

Zoology,  among  the  Greeks  and 
Romans,  437  ;  definition  of,  436  ; 
definition  of  economic,  436;  of 
the  sixteenth  century,  441 ;  of  the 
seventeenth  century,  442;  of  the 
eighteenth  century,  443;  of  the 
nineteenth  century,  445;  system- 
atic, 436 


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SEP  2  0  J939 

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LD  21-100ra-8,'34 

f~-<. 


.BIOLOGY 

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(7 

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